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[Java教程][LeetCode] Symmetric Tree


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

For example, this binary tree is symmetric:

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

 

But the following is not:

  1  / \ 2  2  \  \  3  3

     这道题也挺有意思的。不过首先要搞懂题目,首先搞清楚怎样的BTS才算symmetric的。必须要是一个balanced的BTS然后两边的height都相等。

     这道题个人觉得用recursive来写比较容易哈。

     代码如下。~

/** * 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 symhelper(root.left,root.right);  }    public boolean symhelper(TreeNode left,TreeNode right){    if(left==null||right==null){      return (left==right);    }    if((left.val==right.val)&&(symhelper(left.left,right.right))&&(symhelper(left.right,right.left))){      return true;    }else{      return false;    }  }}