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。

 1 /**
 2  * Definition for a binary tree node.
 3  * struct TreeNode {
 4  *     int val;
 5  *     TreeNode *left;
 6  *     TreeNode *right;
 7  *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
 8  * };
 9  */
10 class Solution {
11 public:
12     int closestValue(TreeNode* root, double target) {
13         int res = root->val;
14         if (root->left != NULL && (double)res > target) {
15             int leftRes = closestValue(root->left, target);
16             res = abs(res - target) < abs(leftRes - target) ? res : leftRes;
17         }
18         if (root->right != NULL && (double)res < target) {
19             int rightRes = closestValue(root->right, target);
20             res = abs(res - target) < abs(rightRes - target) ? res : rightRes;
21         }
22         return res;
23     }
24 };