270. Closest Binary Search Tree Value --------E

 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.

Example:

Input: root = [4,2,5,1,3], target = 3.714286

    4
   / \
  2   5
 / \
1   3

Output: 4

A:

就是对比呗。没啥特别的地方

/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode() : val(0), left(nullptr), right(nullptr) {}
 *     TreeNode(int x) : val(x), left(nullptr), right(nullptr) {}
 *     TreeNode(int x, TreeNode *left, TreeNode *right) : val(x), left(left), right(right) {}
 * };
 */
class Solution {
public:
    int closestValue(TreeNode* root, double target) {
        if(target < root->val){
            if(root->left){
                int left = closestValue(root->left, target);
                if(abs(left - target) < abs(target - root->val))
                    return left;
            }
        }
        if(target > root->val){
            if(root->right){
                int right = closestValue(root->right, target);
                if(abs(right - target) < abs(target - root->val))
                    return right;
            }
        }
        return root->val;
    }
};