226.Invert-Binary-Tree

226. Invert Binary Tree

题目地址

https://leetcode.com/problems/invert-binary-tree/

题目描述

Invert a binary tree.

Example:

Input:

     4
   /   \
  2     7
 / \   / \
1   3 6   9
Output:

     4
   /   \
  7     2
 / \   / \
9   6 3   1
Trivia:
This problem was inspired by this original tweet by Max Howell:

Google: 90% of our engineers use the software you wrote (Homebrew), but you can’t invert a binary tree on a whiteboard so f*** off.

代码

Approach #1 Recursion DFS

/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */
class Solution {
  public TreeNode invertTree(TreeNode root) {
      if (root == null)        return null;
    TreeNode right = invertTree(root.right);
    TreeNode left = invertTree(root.left);
    root.left = right;
    root.right = left;
    return root;
  }
}

Approach #2 Iterative BFS

class Solution {
  public TreeNode intervertTree(TreeNode root) {
    if (root == null) return null;
    Queue<TreeNode> queue = new LinkedList();
    queue.add(root);
    while (!queue.isEmpty()) {
      TreeNode current = queue.poll();
      TreeNode tmp = current.left;
      current.left = current.right;
      current.right = tmp;
      if (current.left != null) queue.add(current.left);
      if (current.right != null) queue.add(current.right);
    }

    return root;
  }
}