leetcode16.3Sum Closest

发表于 更新于 分类于 ，

题外话

鉴于这一题的核心思路和leetcode15的思路相同，可以先写一下15题并参考一下我之前的一篇博客

题目要求

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

1
2
3
For example, given array S = {-1 2 1 -4}, and target = 1.

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

翻译过来就是，假设一个有n的元素的整数数组S，从S中找到三个值，这三个值的距离输入的目标值最近。返回这三个值的和。

思路一：三指针

这里的思路和leetcode15是一样的，就是用三个指针获得三个值并计算他们的和。不同的是和当前的最小距离比较，代码如下

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
public int threeSumClosest(int[] nums, int target) {
    Arrays.sort(nums);
    int length = nums.length;
    int closest = nums[0]+nums[1]+nums[2] - target;
    for(int i = 0 ; i<length-2 ; ){
        for(int j = i+1, k = length-1 ; j<k ; ){
            int value = nums[i] + nums[j] + nums[k] - target;
            if(value<0){
                while(nums[j]==nums[++j] && j < k);
            }
            if(value>0){
                while(nums[k--] == nums[k] && j < k);
            }
            if(value==0){
                return target;
            }
            if(Math.abs(value) < Math.abs(closest)){
                closest = value;
            }        
        }
        while(nums[i] == nums[++i] && i < nums.length - 2);
    }
        
    return closest + target;
}

思路二：hashmap等

同leetcode15，请直接参考我的博客