力扣——对称二叉树

谁践踏了优雅 2023-10-02 13:46 31阅读 0赞

##### [对称二叉树][Link 1] #####

给定一个二叉树，检查它是否是镜像对称的。

例如，二叉树 \[1,2,2,3,4,4,3\] 是对称的。

/  
2 2  
/ \\ /  
3 4 4 3

但是下面这个 \[1,2,2,null,3,null,3\] 则不是镜像对称的:

/  
2 2  
\\  
3 3

进阶：

你可以运用递归和迭代两种方法解决这个问题吗？

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

--------------------

package com.kk;
    
    public class IsSymmetric {
        
        public boolean isSymmetric(TreeNode root) {
        
            return check(root, root);
        }
    
        public boolean check(TreeNode p, TreeNode q) {
        
            if (p == null && q == null) {
        
                return true;
            }
            if (p == null || q == null) {
        
                return false;
            }
            return p.val == q.val && check(p.left, q.right) && check(p.right, q.left);
        }
        public class TreeNode {
        
          int val;
          TreeNode left;
          TreeNode right;
          TreeNode() {
        }
          TreeNode(int val) {
         this.val = val; }
          TreeNode(int val, TreeNode left, TreeNode right) {
        
              this.val = val;
              this.left = left;
              this.right = right;
          }
      }
    }

[Link 1]: https://leetcode-cn.com/problems/symmetric-tree/