LeetCode刷题（C++）——Symmetric Tree（Easy）

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

/** * 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==NULL)          return true;        return isSymmetric(root,root);    }        bool isSymmetric(TreeNode* pRoot1, TreeNode* pRoot2)    {        if(pRoot1==NULL&&pRoot2==NULL)          return true;        if(pRoot1==NULL||pRoot2==NULL)          return false;        if(pRoot1->val!=pRoot2->val)          return false;        return isSymmetric(pRoot1->left,pRoot2->right)&&isSymmetric(pRoot1->right,pRoot2->left);    }};