[leetcode]101. Symmetric Tree对称树

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.

 

题目

给定二叉树，判断其是否左右对称

 

思路

DFS

 

代码

1 /* 2 Time:O(n)， 3 Space: O(logn) 即 O(h) 树的deepest hight 4 */ 5 public class Solution { 6 public boolean isSymmetric(TreeNode root) { 7 if (root == null) return true; 8 return isSymmetric(root.left, root.right); 9 } 10 private static boolean isSymmetric(TreeNode p, TreeNode q) { 11 if (p == null && q == null) return true; // 终止条件 12 if (p == null || q == null) return false; // 终止条件 13 return p.val == q.val // 三方合并 14 && isSymmetric(p.left, q.right) 15 && isSymmetric(p.right, q.left); 16 } 17 }

 

转载于:https://www.cnblogs.com/liuliu5151/p/9825075.html