[leetcode]Symmetric Tree

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

DFS 对称的比较每个节点的值

/** * Definition for binary tree * struct TreeNode { *     int val; *     TreeNode *left; *     TreeNode *right; *     TreeNode(int x) : val(x), left(NULL), right(NULL) {} * }; */class Solution {public:    bool judge(TreeNode *ltree,TreeNode *rtree){        bool ans ;        if(ltree == NULL && rtree == NULL) return true;        if(ltree == NULL ^  rtree == NULL) return false;        ans = (ltree->val==rtree->val)&&judge(ltree->left,rtree->right)&&judge(ltree->right,rtree->left);        return ans;    }    bool isSymmetric(TreeNode *root) {        if(root == NULL) return true;        return  judge(root->left,root->right);    }};