/*
struct TreeNode {
    int val;
    struct TreeNode *left;
    struct TreeNode *right;
    TreeNode(int x) :
            val(x), left(NULL), right(NULL) {
    }
};
*/
class Solution {
public:
    bool isSymmetrical(TreeNode* pRoot) {
        return dfs(pRoot, pRoot);
    }

    bool dfs(TreeNode *L, TreeNode *R) {
        if((L && !R) || (!L && R))    return false;
        if(!L && !R)    return true;
        if(L->val != R->val)    return false;
        return dfs(L->left, R->right) && dfs(L->right, R->left);
    }
};