270. Closest Binary Search Tree Value

• Difficulty: Easy

• Topics: Binary Search, Tree

• Similar Questions:

  • Count Complete Tree Nodes

  • Closest Binary Search Tree Value II

  • Search in a Binary Search Tree

Problem:

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

Solutions:

/**
 * 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 ret = root->val;
        if (root->left) {
            int leftClose = closestValue(root->left, target);
            if (abs(ret - target) > abs(leftClose - target)) {
                ret = leftClose;
            }
        }

        if (root->right) {
            int rightClose = closestValue(root->right, target);
            if (abs(ret - target) > abs(rightClose - target)) {
                ret = rightClose;
            }
        }

        return ret;
    }
};