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Commit 435e5c3

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added Invert Binary Tree (Easy)
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‎Easy/InvertBinaryTree/README.md‎

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# Invert Binary Tree
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[Leetcode Link](https://leetcode.com/problems/invert-binary-tree/)
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## Problem:
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Invert a binary tree.
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## Example:
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```
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Input:
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4
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/ \
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2 7
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/ \ / \
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1 3 6 9
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Output:
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4
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/ \
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7 2
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/ \ / \
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9 6 3 1
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```

‎Easy/InvertBinaryTree/solution.py‎

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from utils import TreeNode
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class Solution:
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def invertTree(self, root: TreeNode) -> TreeNode:
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# base case: if we hit null child
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if not root:
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return
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# swap left and right child
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temp = root.left
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root.left = root.right
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root.right = temp
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# traverse recursively
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self.invertTree(root.left)
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self.invertTree(root.right)
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return root
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sol = Solution()
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root = TreeNode(4, left=TreeNode(2, left=TreeNode(1), right=TreeNode(
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3)), right=TreeNode(7, left=TreeNode(6), right=TreeNode(9)))
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# root = TreeNode(1)
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# root = None
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# root = TreeNode(1, TreeNode(2))
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print("Before inversion:", root)
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inverted = sol.invertTree(root)
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print("Inverted Tree:", inverted)

‎Easy/InvertBinaryTree/utils.py‎

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# Leetcode Treenode structure and in,pre,postorder and leetcode representation of structure
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class TreeNode:
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def __init__(self, val=0, left=None, right=None):
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self.val = val
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self.left = left
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self.right = right
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# inorder traversal list (left,self,right)
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def inorder(self):
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# recursive helper
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def dfs(node):
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if not node:
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return
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dfs(node.left)
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traversal.append(node.val)
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dfs(node.right)
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traversal = list()
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dfs(self)
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return traversal
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# preorder traversal list (left,self,right)
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def preorder(self):
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# recursive helper
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def bfs(node):
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if not node:
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return
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traversal.append(node.val)
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bfs(node.left)
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bfs(node.right)
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traversal = list()
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bfs(self)
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return traversal
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# postorder traversal list (left,self,right)
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def postorder(self):
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# recursive helper
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def dfs(node):
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if not node:
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return
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dfs(node.left)
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dfs(node.right)
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traversal.append(node.val)
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traversal = list()
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dfs(self)
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return traversal
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# leetcode representation of trees (level-by-level, and explicit None for absence of children)
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def __str__(self):
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tree = list()
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queue = list()
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queue.append(self)
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while queue and not all(node is None for node in queue):
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currentNode = queue.pop(0)
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if currentNode is None:
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tree.append(None)
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else:
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tree.append(currentNode.val)
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queue.append(currentNode.left)
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queue.append(currentNode.right)
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return str(tree)
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# test driver
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if __name__ == "__main__":
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root = TreeNode(1, TreeNode(2, right=TreeNode(4)),
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TreeNode(3, left=TreeNode(5, right=TreeNode(6))))
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print("inorder:", root.inorder())
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print("preorder:", root.preorder())
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print("postorder:", root.postorder())
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print("leetcode:", root)

‎README.md‎

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- [N-ary Tree Postorder Traversal](Easy/NaryTreePostorderTraversal)
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- [Pascal's Triangle](Easy/PascalsTriangle)
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- [Merge Two Binary Trees](Easy/MergeTwoBinaryTrees)
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- [Invert Binary Tree](Easy/InvertBinaryTree)
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- Medium
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- [Minimum Add to Make Parentheses Valid](Medium/MinimumAddtoMakeParenthesesValid)
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- [Distribute Coins in Binary Tree](Medium/DistributionCoinsInBinaryTree)

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