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‎README.md

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# python-data-structures

‎bst.py

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class Node:
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def __init__(self, val, parent):
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self.val = val
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self.leftChild = None
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self.rightChild = None
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self.parent = parent
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self.hasTraversedLeft = False
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self.hasTraversedRight = False
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def __str__(self):
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return "Node(%s)" % self.val
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def get(self):
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return self.val
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def set(self, val):
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self.val = val
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def getChildren(self):
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children = []
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if (self.leftChild != None):
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children.append(self.leftChild)
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if (self.rightChild != None):
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children.append(self.rightChild)
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return children
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def isLeftChild(self):
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if self.parent is None: return False
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return (self.val <= self.parent.val)
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def isRightChild(self):
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if self.parent is None: return False
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return (self.val > self.parent.val)
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# Duplicates are kept as left child of currentNode
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class BST:
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def __init__(self):
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self.root = None
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# def __str__(self):
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# ans = []
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# currentNode = self.root
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# while currentNode
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def setRoot(self, val):
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self.root = Node(val, None)
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def insert(self, val):
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if(self.root is None):
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self.setRoot(val)
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else:
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self.insertNode(self.root, val)
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def insertNode(self, currentNode, val):
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if (val <= currentNode.val):
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if (currentNode.leftChild):
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self.insertNode(currentNode.leftChild, val)
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else:
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currentNode.leftChild = Node(val, currentNode)
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elif (val > currentNode.val):
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if (currentNode.rightChild):
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self.insertNode(currentNode.rightChild, val)
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else:
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currentNode.rightChild = Node(val, currentNode)
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def remove(self, val, startNode=None):
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target = self.find(val, startNode)
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if target is not None:
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if target is self.root:
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if target.leftChild is None and target.rightChild is None:
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self.root = None
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elif target.leftChild is None and target.rightChild is not None:
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self.root = target.rightChild
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elif target.leftChild is not None and target.rightChild is None:
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self.root = target.leftChild
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elif target.leftChild is not None and target.rightChild is not None:
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rightMin = self.min(target.rightChild)
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target.val = rightMin
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self.remove(rightMin, target.rightChild)
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else:
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return False
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return True
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else:
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if target.leftChild is None and target.rightChild is None:
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if target.parent.val > target.val: target.parent.leftChild = None
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elif target.parent.val == target.val: target.parent.rightChild = None
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elif target.parent.val < target.val: target.parent.rightChild = None
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elif target.leftChild is None and target.rightChild is not None:
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if target.parent.val > target.val: target.parent.leftChild = target.rightChild
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elif target.parent.val == target.val: target.parent.rightChild = target.rightChild
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elif target.parent.val < target.val: target.parent.rightChild = target.rightChild
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target.rightChild.parent = target.parent
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elif target.leftChild is not None and target.rightChild is None:
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if target.parent.val > target.val: target.parent.leftChild = target.leftChild
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elif target.parent.val == target.val: target.parent.rightChild = target.leftChild
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elif target.parent.val < target.val: target.parent.rightChild = target.leftChild
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target.leftChild.parent = target.parent
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elif target.rightChild is not None and target.rightChild is not None:
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rightMin = self.min(target.rightChild)
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target.val = rightMin
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self.remove(rightMin, target.rightChild)
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else:
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# Funny edge case
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return False
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return True
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else:
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return False
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def find(self, val, startNode=None):
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# Returns node if found, else None
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return self.findNode(self.root if startNode is None else startNode, val)
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def getPredecessor(self, val):
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n = self.find(val)
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if n is not None:
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# Case 1: Node has a left subtree
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if n.leftChild is not None:
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return self.max(n.leftChild, returnVal=False)
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else:
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# Case 2: Node has no left subtree, it is the left child of its parent
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predecessor = n
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while predecessor.isLeftChild():
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predecessor = predecessor.parent
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# Case 3: Node has no left subtree, it is the right child of its parent
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return predecessor.parent
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else:
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return None
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# Return smallest Node greater than val
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def getSuccessor(self, val):
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n = self.find(val)
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if n is not None:
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# Case 1: Node has a right subtree
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if n.rightChild is not None:
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return self.min(n.rightChild, returnVal=False)
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else:
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# Case 2: Node has no right subtree, it is the right child of its parent
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successor = n
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while successor.isRightChild():
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successor = successor.parent
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# Case 3: Node has no right subtree, it is left child of its parent
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return successor.parent
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else:
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return None
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def findNode(self, currentNode, val):
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if(currentNode is None):
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return None
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elif(val == currentNode.val):
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return currentNode
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elif(val < currentNode.val):
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return self.findNode(currentNode.leftChild, val)
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else:
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return self.findNode(currentNode.rightChild, val)
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def min(self, node=None, returnVal=True):
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if self.root is None: return None
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currentNode = self.root if node is None else node
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while currentNode.leftChild is not None:
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currentNode = currentNode.leftChild
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return currentNode.val if returnVal else currentNode
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def max(self, node=None, returnVal=True):
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if self.root is None: return None
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currentNode = self.root if node is None else node
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while currentNode.rightChild is not None:
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currentNode = currentNode.rightChild
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return currentNode.val if returnVal else currentNode
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# Iterative in-order traversal of nodes
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def sort(self, reverse=False):
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# Returns tree in ascending order
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import copy
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currentNode = copy.deepcopy(self.root)
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while True:
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if currentNode.hasTraversedLeft and currentNode.hasTraversedRight and currentNode.parent is None:
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break
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else:
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if not currentNode.hasTraversedLeft:
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currentNode.hasTraversedLeft = True
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if currentNode.leftChild is not None: currentNode = currentNode.leftChild
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else:
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if not currentNode.hasTraversedRight:
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yield currentNode.val
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currentNode.hasTraversedRight = True
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if currentNode.rightChild is not None: currentNode = currentNode.rightChild
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else:
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currentNode = currentNode.parent
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def test():
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data = [10,4,5,2,3,8,9,9]
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t = BST()
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for i in data:
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t.insert(i)
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# Test sort
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sorted = []
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for i in t.sort():
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sorted.append(i)
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assert(sorted == [2,3,4,5,8,9,9,10])
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# Test min max
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assert(t.min() == 2)
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assert(t.max() == 10)
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t.insert(11)
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assert(t.max() == 11)
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t.insert(-10)
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assert(t.min() == -10)
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# Test find
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assert(t.find(10).val == 10)
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# Test remove
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assert(t.remove(9) == True)
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assert(t.remove(10) == True)
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assert(t.remove(6) == False)
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sorted = []
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for i in t.sort():
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sorted.append(i)
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assert(sorted == [-10, 2, 3, 4, 5, 8, 9, 11])
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# Current state of tree
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# 11
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# /
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# 4
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# / \
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# 2 5
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# / \ \
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#-10 3 8
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# \
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# 9
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# Test getSuccessor
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assert(t.getSuccessor(4).val == 5)
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assert(t.getSuccessor(2).val == 3)
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assert(t.getSuccessor(3).val == 4)
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assert(t.getSuccessor(9).val == 11)
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assert(t.getSuccessor(-10).val == 2)
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assert(t.getSuccessor(15) == None)
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assert(t.getSuccessor(11) == None)
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# Test getPredecessor
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assert(t.getPredecessor(4).val == 3)
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assert(t.getPredecessor(2).val == -10)
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assert(t.getPredecessor(3).val == 2)
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assert(t.getPredecessor(5).val == 4)
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assert(t.getPredecessor(9).val == 8)
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assert(t.getPredecessor(-10) == None)
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assert(t.getPredecessor(11).val == 9)
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assert(t.getPredecessor(15) == None)
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if __name__ == "__main__":
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test()

‎fenwick_tree.py

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# A 1-indexed Bit Indexed Tree or Fenwick Tree
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class FenwickTree:
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def __init__(self, a):
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for (idx,v) in enumerate(a):
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nextIdx = (idx+1) + lowestSetBit(idx+1) - 1
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if nextIdx < len(a):
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a[nextIdx] += v
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self.tree = a
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def __str__(self):
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return str(self.tree)
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# Find the sum of elements from start of array to end
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def prefixSum(self, end):
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ans = 0
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while end > 0:
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ans += self.tree[end-1]
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end -= lowestSetBit(end)
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return ans
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# Find the sum of elements from start to end inclusive
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def range(self, start, end):
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if start < 1:
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raise Exception("Starting index must be at least 1.")
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if end < start:
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raise Exception("End index must be greater than or equal to start")
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return self.prefixSum(end) - self.prefixSum(start-1)
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# idx is based on a 1-based array
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def update(self, idx, value):
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if idx < 1:
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raise Exception("Invalid index, must be at least 1")
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delta = value - self.tree[idx-1]
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while idx <= len(self.tree):
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self.tree[idx-1] += delta
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idx += lowestSetBit(idx)
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def lowestSetBit(intType):
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return (intType & -intType)
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def test():
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import copy
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a = [1,2,3,4,5,6,7,8,9,10]
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tree = FenwickTree(copy.deepcopy(a))
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assert(tree.tree == [1,3,3,10,5,11,7,36,9,19])
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# print(tree)
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assert(tree.prefixSum(1) == 1)
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assert(tree.prefixSum(10) == 55)
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assert(tree.prefixSum(0) == 0)
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assert(tree.prefixSum(-1) == 0)
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assert(tree.range(1,4) == 10)
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assert(tree.range(2,5) == 14)
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assert(tree.range(5, 10) == 45)
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tree.update(1, 10)
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assert(tree.tree == [10,12,3,19,5,11,7,45,9,19])
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assert(tree.range(1,4) == 19)
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assert(tree.range(2,5) == 14)
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assert(tree.range(5, 10) == 45)
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if __name__ == "__main__":
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test()

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