leetcode

LeetCode 270. Closest Binary Search Tree Value

Problem

LeetCode 270. Closest Binary Search Tree Value

1. 题目简述

给出一颗二叉树，给出一个目标double类型的target，找出与其最近的节点值。例如：

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

    4
   / \
  2   5
 / \
1   3

Output: 4

2. 算法思路

中序遍历

这道题和LeetCode 272看起来很像，只不过272是要求k个最接近的数。

这道题只用找一个最接近的数，很简单，直接中序遍历，愿意加一个判断本次和上一次差值不同剪枝条件也可以，我没加。

3. 解法

  1. 中序遍历，用abs函数记录绝对值，closestValue记录最接近的值

/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode() {}
 *     TreeNode(int val) { this.val = val; }
 *     TreeNode(int val, TreeNode left, TreeNode right) {
 *         this.val = val;
 *         this.left = left;
 *         this.right = right;
 *     }
 * }
 */
class Solution {
    public int closestValue(TreeNode root, double target) {
        double abs = Double.MAX_VALUE;
        int closestValue = 0;

        while (root != null) {
            double diff = target - (double)root.val;
            if (Math.abs(diff) < abs) {
                closestValue = root.val;
                abs = Math.abs(diff);
            }
            if (diff > 0) {
                root = root.right;
            } else if (diff < 0) {
                root = root.left;
            } else {
                return root.val;
            }
        }

        return closestValue;
    }
}