Leetcode -- 3 sum closest.

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问题链接：https://oj.leetcode.com/problems/3sum-closest/

问题描述：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.

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).

API : public int threeSumClosest(int[] num, int target)

分析：这题和3 sum基本是同一题，唯一不同之处在于上一题是维护一组答案，这一次是维护一个答案，所以也不详细解读了，看代码吧：

    public int threeSumClosest(int[] num, int target) {        Arrays.sort(num);        int res = Integer.MAX_VALUE;        for(int i = 0; i < num.length; i++){            if(i > 0 && num[i] == num[i - 1])                continue;            int head = i + 1;            int tail = num.length - 1;            while(head < tail){                if(head != i + 1 && num[head] == num[head - 1]){                    head++;                    continue;                }                if(tail != num.length - 1 && num[tail] == num[tail + 1]){                    tail--;                    continue;                }                res = Math.abs(res) > Math.abs(num[i] + num[head] + num[tail] - target) ? (num[i] + num[head] + num[tail] - target) : res;                if(num[i] + num[head] + num[tail] > target){                    tail--;                }else if(num[i] + num[head] + num[tail] < target){                    head++;                }else{                    return target;                }            }        }        return res + target;    }

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