226_InvertBinaryTree.py

import collections
# Definition for a binary tree node.
class TreeNode:
    def __init__(self, x):
        self.val = x
        self.left = None
        self.right = None


def stringToTreeNode(input):
    input = input.strip()
    input = input[1:-1]
    if not input:
        return None

    inputValues = [s.strip() for s in input.split(',')]
    root = TreeNode(int(inputValues[0]))
    nodeQueue = [root]
    front = 0
    index = 1
    while index < len(inputValues):
        node = nodeQueue[front]
        front = front + 1

        item = inputValues[index]
        index = index + 1
        if item != "null":
            leftNumber = int(item)
            node.left = TreeNode(leftNumber)
            nodeQueue.append(node.left)

        if index >= len(inputValues):
            break

        item = inputValues[index]
        index = index + 1
        if item != "null":
            rightNumber = int(item)
            node.right = TreeNode(rightNumber)
            nodeQueue.append(node.right)
    return root


def treeNodeToString(root):
    if not root:
        return "[]"
    output = ""
    queue = [root]
    current = 0
    while current != len(queue):
        node = queue[current]
        current = current + 1

        if not node:
            output += "null, "
            continue

        output += str(node.val) + ", "
        queue.append(node.left)
        queue.append(node.right)
    return "[" + output[:-2] + "]"


class Solution:
    # recursively
    def invertTree1(self, root):
        if root:
            root.left, root.right = self.invertTree(root.right), self.invertTree(root.left)
            return root
    # BFS
    def invertTree2(self, root):
        queue = collections.deque([(root)])
        while queue:
            node = queue.popleft()
            if node:
                node.left, node.right = node.right, node.left
                queue.append(node.left)
                queue.append(node.right)
        return root
    # DFS
    def invertTree(self, root: TreeNode) -> TreeNode:
        stack = [root]
        while stack:
            node = stack.pop()
            if node:
                node.left, node.right = node.right, node.left
                stack.extend([node.right, node.left])
        return root

def main():
    root = stringToTreeNode("[4,2,7,1,3,6,9]")
    ret = Solution().invertTree2(root)
    out = treeNodeToString(ret)
    # Output:
    #      4
    #    /   \
    #   7     2
    #  / \   / \
    # 9   6 3   1
    print(out)


if __name__ == '__main__':
    main()