Symmetric Tree

发布时间：2020-12-14 04:30:07 所属栏目：大数据来源：网络整理

导读：Given a binary tree,check whether it is a mirror of itself (ie,symmetric around its center). For example,this binary tree? [1,2,3,4,3] ?is symmetric: 1 / 2 2 / / 3 4 4 3 ? But the following? [1,null,3] ?is not: 1 / 2 2 3 3 ? Note: Bonu

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

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

    1
   /   2   2
 /  / 3  4 4  3

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

    1
   /   2   2
         3    3

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

Approach #1: C++.

/**
 * 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;
        
        Stack<TreeNode> stack = new Stack<TreeNode>();
        
    }
}

（编辑：李大同）

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