Invert Binary Tree 二叉树反转

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

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


/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */
public class Solution {
    TreeNode temp;
    public TreeNode invertTree(TreeNode root) {
        if(root!=null){
            temp=root.left;
            root.left=root.right;
            root.right=temp;
            if(root.left!=null)  invertTree(root.left); //注意递归哦
            if(root.right!=null)  invertTree(root.right);
        }
        return root;//涵盖了root==null的情况
    }
}