LeetCode Validate Binary Search Tree

天若有情天亦老，人间正道是沧桑。输了，在那没考虑全面甚至没去考虑全面而提交的一刻就输了，再回首，正是那年似曾相识的题目，躲在旮旯深处！

错了之后一想，记忆清晰呀，微策略面试题，在家里面试的，做之前却没想起来。所以还是原样子错过了。这题就是这么一个陷阱，明白了绕过来就行了。

bool isLeftRight(TreeNode *root,int &Biggest,int &Smallest) {if(root==NULL)return true;int leftBiggest,leftSmallest;if (root->left){if(root->val <= root->left->val)return false;if(!isLeftRight(root->left,leftBiggest,leftSmallest))return false;if(leftBiggest>=root->val)return false;}else{leftBiggest = leftSmallest = root->val;}int rightBiggest,rightSmallest;if (root->right){if(root->val >= root->right->val)return false;if(!isLeftRight(root->right,rightBiggest,rightSmallest))return false;if(rightSmallest<=root->val)return false;}else{rightBiggest = rightSmallest = root->val;}Biggest = leftBiggest>rightBiggest?leftBiggest:rightBiggest;Smallest = leftSmallest<rightSmallest?leftSmallest:rightSmallest;return true;}