16.3Sum Closest

题目描述

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.

Example:
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).

思路分析

这题和求三个数之和为定值的思路相似。不同之处在与求最接近target的三个数。排序后，我们可以先设定ans = nums[0]+nums[1]+nums[2]，然后依次遍历，对于任意组合的三个数值，他们的和sum和target差的绝对值与ans与target差的绝对值相比较，不断更新ans，使得其保持最小值。

代码

public int threeSumClosest(int[] nums, int target) {        Arrays.sort(nums);        int ans = nums[0]+nums[1]+nums[2];        int len = nums.length;        int sum = 0;        for (int i = 0; i < len-2; i++) {            int j = i+1,k = len-1;            while(j<k)            {                sum = nums[i]+nums[j]+nums[k];                if(Math.abs(sum-target)<Math.abs(ans-target))                {                    ans = sum;                }                if(sum>target)                    k--;                else                    j++;            }        }        return ans;    }