LeetCode算法题目：Symmetric Tree

题目：

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

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分析：

递归，保存左右两个节点，然后判断leftNode->left和rightNode->right，以及leftNode->right和rightNode->left。如此不断递归

代码：

/** * Definition for a binary tree node. * struct TreeNode { * int val; * TreeNode *left; * TreeNode *right; * TreeNode(int x) : val(x), left(NULL), right(NULL) {} * }; */ class Solution { public: bool isSymmetric(TreeNode *root) { if(!root) return true; return compRoot(root -> left, root -> right); } private: bool compRoot(TreeNode* lroot, TreeNode* rroot){ if(!lroot) return (NULL == rroot); if(NULL == rroot) return false; if(lroot -> val != rroot -> val) return false; return (compRoot(lroot -> left, rroot -> right) && compRoot(lroot -> right, rroot -> left)); } };