题目

题目链接：
https://www.lintcode.com/problem/468/description?showListFe=true&page=1&problemTypeId=2&tagIds=371&ordering=id&pageSize=50

思路

递归

Java代码

/**
 * Definition of TreeNode:
 * public class TreeNode {
 *     public int val;
 *     public TreeNode left, right;
 *     public TreeNode(int val) {
 *         this.val = val;
 *         this.left = this.right = null;
 *     }
 * }
 */

public class Solution {
    /**
     * @param root: the root of binary tree.
     * @return: true if it is a mirror of itself, or false.
     */
    public boolean isSymmetric(TreeNode root) {
        if(root ==null) return true;
        return f(root.left,root.right);
    }

    public boolean f(TreeNode  a,TreeNode b){
        if(a==null && b==null) return true;
        if(a==null || b==null) return false;

        if(a.val!=b.val) return false;

        return f(a.left,b.right) && f(a.right,b.left);
    }
}