Closest Binary Search Tree Value -- LeetCode

Given a non-empty binary search tree and a target value, find the value in the BST that is closest to the target.

Note:

• Given target value is a floating point.
• You are guaranteed to have only one unique value in the BST that is closest to the target.

思路：递归求解。因为是二叉搜索树，我们不需要遍历所有的节点，通过prune来提高速度。

 /**
  * 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:
     int closestValue(TreeNode* root, double target) {
         int res = root->val;
         if (root->left != NULL && (double)res > target) {
             int leftRes = closestValue(root->left, target);
             res = abs(res - target) < abs(leftRes - target) ? res : leftRes;
         }
         if (root->right != NULL && (double)res < target) {
             int rightRes = closestValue(root->right, target);
             res = abs(res - target) < abs(rightRes - target) ? res : rightRes;
         }
         return res;
     }
 };