LeetCode|3SUM Closest

题目

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.

    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

和3SUM的思路类似。先排序，然后用一个指针指向一个位置，然后用2个指针分别指向剩下的部分头和尾。定义个closest，表示和target最接近的。但是如果closest比target还大，那么就要分情况移动剩下的指针。情况一.3个数的和比target小，那么只能移动begin指针，情况二.3个数的和比target大，那么只能移动end指针.好了，题目结束.

代码

public class Solution {    public int threeSumClosest(int[] num, int target) {        Arrays.sort(num);        int result = -1;        int closest = Integer.MAX_VALUE;                for(int i = 0 ; i <=num.length -3 ; i++)        {        int begin = i+1;        int end = num.length-1;                while(begin<end)        {        if(closest>Math.abs((num[i] + num[begin] + num[end]-target)))        {        closest = Math.abs((num[i] + num[begin] + num[end]-target));        result = num[i]+num[begin]+num[end];        }        else if(num[i]+num[begin]+num[end] < target)        {        begin++;                }        else        {        end--;        }        }        }        return result;    }}