leetcode226 - Invert Binary Tree - easy

Invert a binary tree.

Example:

Input:

     4

   /   \

  2     7

/ \   / \

1   3 6   9

Output:

     4

   /   \

  7     2

/ \   / \

9   6 3   1

 

 

分治法

1.解决自己小三角，交换左右直接孩子。

2.递归，让自己的左右孩子也去做这件事情。 

 

实现：

/**
 * 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 root;
        }
        invertTree(root.left);
        invertTree(root.right);
        TreeNode temp = root.left;
        root.left = root.right;
        root.right = temp;
        return root;
    }
}