【LeetCode】 101. Symmetric Tree 对称二叉树（Easy）（JAVA）

【LeetCode】 101. Symmetric Tree 对称二叉树（Easy）（JAVA）

题目地址: https://leetcode.com/problems/symmetric-tree/

题目描述：

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

Follow up: Solve it both recursively and iteratively.

题目大意

给定一个二叉树，检查它是否是镜像对称的。

解题方法

1、采用递归方法
2、找出递归的条件，left.left == right.right，left.right == right.left

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

    public boolean iH(TreeNode left, TreeNode right) {
        if (left == null || right == null) return left == right;
        return left.val == right.val && iH(left.left, right.right) && iH(left.right, right.left);
    }
}

执行用时 : 0 ms, 在所有 Java 提交中击败了 100.00% 的用户
内存消耗 : 37.8 MB, 在所有 Java 提交中击败了 36.25% 的用户