Leetcode NO.270 Closest Binary Search Tree Value

本题题目要求如下：

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.

本题难度不算太高，Easy里面的中等水平。。其实跟别的BST一样，就是如果root比target小，向右，否则向左，然后每次都要记录一下差值，如果差值小于0.5，则停止，这必须就是最优解！

代码如下：

/**
 * 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;
        while (root != nullptr) {
            if (abs(root->val - target) < 0.5) {
                return root->val;
            }
            if (abs(root->val - target) < abs(res - target)) {
                res = root->val;
            }
            if (root->val < target) {
                root = root->right;
            }
            else {
                root = root->left;
            }
        }
        return res;
    }
};