16. 3Sum Closest

最新推荐文章于 2025-08-23 19:36:46 发布

转载最新推荐文章于 2025-08-23 19:36:46 发布 · 53 阅读

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原文链接：https://segmentfault.com/a/1190000018116543

文章标签：

#java #runtime

本文介绍了一种解决三数之和最接近目标问题的高效算法，通过先排序再使用双指针技术，实现对整数数组中寻找三个数之和最接近给定目标值的解决方案。该算法在Java在线提交中表现优秀，运行时间为10ms，优于86.09%的提交，内存使用为27MB。

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Given an array nums of n integers and an integer target, find three integers in nums such that the sum is closest to target. Return the sum of the three integers. You may assume that each input would have exactly one solution.

Example:

Given array nums = [-1, 2, 1, -4], and target = 1.

The sum that is closest to the target is 2. (-1 + 2 + 1 = 2).

难度：medium

题目：
给定一整数数组和一整数，找出三个数之和最接近目标整数并返回其和。假定输入只有一个匹配的答案。

思路：先排序，固定一个数，然后剩下的数组两边夹挤。

Runtime: 10 ms, faster than 86.09% of Java online submissions for 3Sum Closest.
Memory Usage: 27 MB, less than 16.46% of Java online submissions for 3Sum Closest.

class Solution {
    public int threeSumClosest(int[] nums, int target) {
        Arrays.sort(nums);
        int n = nums.length;
        int result = nums[0] + nums[1] + nums[2];
        int distance = Math.abs(result - target); 
        for (int i = 0; i < n - 2; i++) {
            int left = i + 1;
            int right = n - 1;
            while (left < right) {
                int sum = nums[i] + nums[left] + nums[right];
                if (sum == target) {
                    return target;
                }
                if (sum > target) {
                    right--;
                } else {
                    left++;
                }
                
                if (Math.abs(sum - target) < Math.abs(distance)) {
                    distance = Math.abs(sum - target);
                    result = sum;
                }
            }
        }
        
        return result;
    }
}