题解 | #对称的二叉树#

/*
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) {
        if (pRoot == NULL) return true;
        return cmp(pRoot->left, pRoot->right);
    }
    bool cmp(TreeNode* left, TreeNode* right) {
        if (left && right == NULL) return false;
        else if (left == NULL && right) return false;
        else if (left == NULL && right == NULL) return true;
        else if (left->val != right->val) return false;

        bool outside = cmp(left->left, right->right);  // 左子树的外侧，右子树的外侧
        bool inside = cmp(left->right, right->left);	// 左子树的内侧，右子树的内侧
        return outside && inside;
    }

};