[LeetCode] 270. Closest Binary Search Tree Value

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

最接近的二叉搜索树的值。题意是给一个二叉树和一个target值（会是一个浮点数），请找出二叉树里面val最接近这个target的node。

递归的思路我没有想得非常清楚所以我这里只给出迭代的做法。因为是BST所以会简单很多，根据target与root节点比较的大小情况来决定到底往左子树走还是往右子树走。

时间O(logn) - 因为每次只会往树的一边走

空间 - O(1)

Java实现

class Solution {
    public int closestValue(TreeNode root, double target) {
        int res = root.val;
        while (root != null) {
            if (Math.abs(target - root.val) < Math.abs(target - res)) {
                res = root.val;
            }
            root = root.val > target ? root.left : root.right;
        }
        return res;
    }
}

JavaScript实现

/**
 * @param {TreeNode} root
 * @param {number} target
 * @return {number}
 */
var closestValue = function (root, target) {
    let res = root.val;
    while (root !== null) {
        if (Math.abs(root.val - target) < Math.abs(res - target)) {
            res = root.val;
        }
        root = root.val > target ? root.left : root.right;
    }
    return res;
};

LeetCode 题目总结