Solution.java

package Tree.easy.No_226_Invert_Binary_Tree;


import Tree.TreeNode;

import java.util.LinkedList;
import java.util.Queue;

/**
 * FileName: Solution
 * Author:   EdisonLi的家用MacBook Pro
 * Date:     2019-03-09 20:40
 * Description: Average of Levels in Binary Tree
 * 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.
 */

public class Solution {
    public TreeNode invertTree(TreeNode root) {
        if (root == null) return root;
        TreeNode rightNode = invertTree(root.right);
        TreeNode leftNode = invertTree(root.left);

        root.right = leftNode;
        root.left = rightNode;

        return root;
    }

    public TreeNode invertTree1(TreeNode root){
        if (root == null) return root;
        Queue<TreeNode> queue = new LinkedList<>();
        queue.add(root);
        while (!queue.isEmpty()){
            TreeNode node = queue.poll();
            TreeNode tem = node.left;
            node.left = node.right;
            node.right = tem;
            if (node.left != null) queue.add(node.left);
            if (node.right != null) queue.add(node.right);
        }
        return root;
    }
}