annotate planemo/lib/python3.7/site-packages/networkx/utils/heaps.py @ 1:56ad4e20f292 draft

"planemo upload commit 6eee67778febed82ddd413c3ca40b3183a3898f1"
author guerler
date Fri, 31 Jul 2020 00:32:28 -0400
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1 """
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2 Min-heaps.
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3 """
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4
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5 __author__ = """ysitu <ysitu@users.noreply.github.com>"""
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6 # Copyright (C) 2014 ysitu <ysitu@users.noreply.github.com>
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7 # All rights reserved.
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8 # BSD license.
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9
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10 from heapq import heappop, heappush
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11 from itertools import count
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12 import networkx as nx
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13
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14 __all__ = ['MinHeap', 'PairingHeap', 'BinaryHeap']
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15
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16
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17 class MinHeap(object):
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18 """Base class for min-heaps.
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19
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20 A MinHeap stores a collection of key-value pairs ordered by their values.
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21 It supports querying the minimum pair, inserting a new pair, decreasing the
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22 value in an existing pair and deleting the minimum pair.
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23 """
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24
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25 class _Item(object):
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26 """Used by subclassess to represent a key-value pair.
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27 """
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28 __slots__ = ('key', 'value')
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29
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30 def __init__(self, key, value):
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31 self.key = key
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32 self.value = value
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33
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34 def __repr__(self):
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35 return repr((self.key, self.value))
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36
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37 def __init__(self):
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38 """Initialize a new min-heap.
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39 """
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40 self._dict = {}
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41
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42 def min(self):
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43 """Query the minimum key-value pair.
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44
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45 Returns
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46 -------
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47 key, value : tuple
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48 The key-value pair with the minimum value in the heap.
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49
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50 Raises
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51 ------
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52 NetworkXError
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53 If the heap is empty.
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54 """
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55 raise NotImplementedError
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56
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57 def pop(self):
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58 """Delete the minimum pair in the heap.
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59
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60 Returns
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61 -------
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62 key, value : tuple
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63 The key-value pair with the minimum value in the heap.
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64
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65 Raises
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66 ------
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67 NetworkXError
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68 If the heap is empty.
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69 """
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70 raise NotImplementedError
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71
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72 def get(self, key, default=None):
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73 """Returns the value associated with a key.
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74
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75 Parameters
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76 ----------
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77 key : hashable object
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78 The key to be looked up.
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79
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80 default : object
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81 Default value to return if the key is not present in the heap.
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82 Default value: None.
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83
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84 Returns
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85 -------
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86 value : object.
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87 The value associated with the key.
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88 """
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89 raise NotImplementedError
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90
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91 def insert(self, key, value, allow_increase=False):
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92 """Insert a new key-value pair or modify the value in an existing
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93 pair.
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94
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95 Parameters
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96 ----------
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97 key : hashable object
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98 The key.
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99
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100 value : object comparable with existing values.
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101 The value.
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102
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103 allow_increase : bool
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104 Whether the value is allowed to increase. If False, attempts to
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105 increase an existing value have no effect. Default value: False.
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106
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107 Returns
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108 -------
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109 decreased : bool
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110 True if a pair is inserted or the existing value is decreased.
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111 """
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112 raise NotImplementedError
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113
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114 def __nonzero__(self):
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115 """Returns whether the heap if empty.
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116 """
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117 return bool(self._dict)
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118
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119 def __bool__(self):
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120 """Returns whether the heap if empty.
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121 """
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122 return bool(self._dict)
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123
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124 def __len__(self):
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125 """Returns the number of key-value pairs in the heap.
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126 """
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127 return len(self._dict)
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128
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129 def __contains__(self, key):
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130 """Returns whether a key exists in the heap.
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131
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132 Parameters
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133 ----------
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134 key : any hashable object.
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135 The key to be looked up.
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136 """
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137 return key in self._dict
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138
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139
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140 def _inherit_doc(cls):
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141 """Decorator for inheriting docstrings from base classes.
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142 """
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143 def func(fn):
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144 fn.__doc__ = cls.__dict__[fn.__name__].__doc__
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145 return fn
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146 return func
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147
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148
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149 class PairingHeap(MinHeap):
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150 """A pairing heap.
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151 """
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152
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153 class _Node(MinHeap._Item):
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154 """A node in a pairing heap.
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155
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156 A tree in a pairing heap is stored using the left-child, right-sibling
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157 representation.
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158 """
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159 __slots__ = ('left', 'next', 'prev', 'parent')
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160
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161 def __init__(self, key, value):
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162 super(PairingHeap._Node, self).__init__(key, value)
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163 # The leftmost child.
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164 self.left = None
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165 # The next sibling.
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166 self.next = None
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167 # The previous sibling.
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168 self.prev = None
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169 # The parent.
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170 self.parent = None
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171
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172 def __init__(self):
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173 """Initialize a pairing heap.
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174 """
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175 super(PairingHeap, self).__init__()
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176 self._root = None
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177
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178 @_inherit_doc(MinHeap)
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179 def min(self):
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180 if self._root is None:
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181 raise nx.NetworkXError('heap is empty.')
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182 return (self._root.key, self._root.value)
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183
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184 @_inherit_doc(MinHeap)
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185 def pop(self):
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186 if self._root is None:
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187 raise nx.NetworkXError('heap is empty.')
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188 min_node = self._root
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189 self._root = self._merge_children(self._root)
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190 del self._dict[min_node.key]
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191 return (min_node.key, min_node.value)
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192
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193 @_inherit_doc(MinHeap)
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194 def get(self, key, default=None):
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195 node = self._dict.get(key)
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196 return node.value if node is not None else default
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197
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198 @_inherit_doc(MinHeap)
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199 def insert(self, key, value, allow_increase=False):
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200 node = self._dict.get(key)
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201 root = self._root
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202 if node is not None:
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203 if value < node.value:
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204 node.value = value
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205 if node is not root and value < node.parent.value:
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206 self._cut(node)
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207 self._root = self._link(root, node)
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208 return True
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209 elif allow_increase and value > node.value:
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210 node.value = value
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211 child = self._merge_children(node)
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212 # Nonstandard step: Link the merged subtree with the root. See
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213 # below for the standard step.
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214 if child is not None:
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215 self._root = self._link(self._root, child)
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216 # Standard step: Perform a decrease followed by a pop as if the
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217 # value were the smallest in the heap. Then insert the new
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218 # value into the heap.
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219 # if node is not root:
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220 # self._cut(node)
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221 # if child is not None:
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222 # root = self._link(root, child)
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223 # self._root = self._link(root, node)
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224 # else:
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225 # self._root = (self._link(node, child)
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226 # if child is not None else node)
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227 return False
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228 else:
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229 # Insert a new key.
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230 node = self._Node(key, value)
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231 self._dict[key] = node
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232 self._root = self._link(root, node) if root is not None else node
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233 return True
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234
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235 def _link(self, root, other):
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236 """Link two nodes, making the one with the smaller value the parent of
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237 the other.
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238 """
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239 if other.value < root.value:
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240 root, other = other, root
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241 next = root.left
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242 other.next = next
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243 if next is not None:
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244 next.prev = other
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245 other.prev = None
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246 root.left = other
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247 other.parent = root
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248 return root
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249
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250 def _merge_children(self, root):
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251 """Merge the subtrees of the root using the standard two-pass method.
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252 The resulting subtree is detached from the root.
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253 """
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254 node = root.left
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255 root.left = None
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256 if node is not None:
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257 link = self._link
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258 # Pass 1: Merge pairs of consecutive subtrees from left to right.
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259 # At the end of the pass, only the prev pointers of the resulting
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260 # subtrees have meaningful values. The other pointers will be fixed
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261 # in pass 2.
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262 prev = None
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263 while True:
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264 next = node.next
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265 if next is None:
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266 node.prev = prev
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267 break
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268 next_next = next.next
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269 node = link(node, next)
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270 node.prev = prev
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271 prev = node
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272 if next_next is None:
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273 break
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274 node = next_next
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275 # Pass 2: Successively merge the subtrees produced by pass 1 from
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276 # right to left with the rightmost one.
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277 prev = node.prev
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278 while prev is not None:
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279 prev_prev = prev.prev
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280 node = link(prev, node)
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281 prev = prev_prev
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282 # Now node can become the new root. Its has no parent nor siblings.
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283 node.prev = None
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284 node.next = None
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285 node.parent = None
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286 return node
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287
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288 def _cut(self, node):
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289 """Cut a node from its parent.
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290 """
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291 prev = node.prev
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292 next = node.next
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293 if prev is not None:
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294 prev.next = next
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295 else:
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296 node.parent.left = next
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297 node.prev = None
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298 if next is not None:
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299 next.prev = prev
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300 node.next = None
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301 node.parent = None
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302
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303
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304 class BinaryHeap(MinHeap):
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305 """A binary heap.
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306 """
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307
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308 def __init__(self):
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309 """Initialize a binary heap.
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310 """
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311 super(BinaryHeap, self).__init__()
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312 self._heap = []
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313 self._count = count()
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314
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315 @_inherit_doc(MinHeap)
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316 def min(self):
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317 dict = self._dict
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318 if not dict:
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319 raise nx.NetworkXError('heap is empty')
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320 heap = self._heap
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321 pop = heappop
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322 # Repeatedly remove stale key-value pairs until a up-to-date one is
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323 # met.
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324 while True:
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325 value, _, key = heap[0]
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326 if key in dict and value == dict[key]:
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327 break
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328 pop(heap)
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329 return (key, value)
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330
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331 @_inherit_doc(MinHeap)
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332 def pop(self):
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333 dict = self._dict
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334 if not dict:
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335 raise nx.NetworkXError('heap is empty')
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336 heap = self._heap
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337 pop = heappop
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338 # Repeatedly remove stale key-value pairs until a up-to-date one is
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339 # met.
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340 while True:
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341 value, _, key = heap[0]
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342 pop(heap)
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343 if key in dict and value == dict[key]:
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344 break
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345 del dict[key]
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346 return (key, value)
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347
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348 @_inherit_doc(MinHeap)
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349 def get(self, key, default=None):
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350 return self._dict.get(key, default)
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351
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352 @_inherit_doc(MinHeap)
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353 def insert(self, key, value, allow_increase=False):
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354 dict = self._dict
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355 if key in dict:
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356 old_value = dict[key]
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357 if value < old_value or (allow_increase and value > old_value):
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358 # Since there is no way to efficiently obtain the location of a
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359 # key-value pair in the heap, insert a new pair even if ones
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360 # with the same key may already be present. Deem the old ones
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361 # as stale and skip them when the minimum pair is queried.
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362 dict[key] = value
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363 heappush(self._heap, (value, next(self._count), key))
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364 return value < old_value
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365 return False
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366 else:
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367 dict[key] = value
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368 heappush(self._heap, (value, next(self._count), key))
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369 return True