LeetCode-101-Symmetric Tree(判断是否为对称树)

Q:

Given a binary tree, check whether it is a mirror of itself (ie, symmetric around its center).

For example, this binary tree [1,2,2,3,4,4,3] is symmetric:

    1   / \  2   2 / \ / \3  4 4  3

But the following [1,2,2,null,3,null,3] is not:

    1   / \  2   2   \   \   3    3

Note:
Bonus points if you could solve it both recursively and iteratively.

Analysis:

可以采用递归的方法，进行一重一重地判断。

Code:

/** * Definition for a binary tree node. * public class TreeNode { *     int val; *     TreeNode left; *     TreeNode right; *     TreeNode(int x) { val = x; } * } */public class Solution {    public boolean isSymmetric(TreeNode root) {        if (root == null) {            return true;        }        return recursiveMethod(root.left, root.right);        }    public static boolean recursiveMethod(TreeNode left, TreeNode right) {        if (left == null && right == null) {            return true;        }        if (left == null || right == null) {            return false;        }        return left.val == right.val && recursiveMethod(left.left, right.right)                && recursiveMethod(left.right, right.left);    }}