Leetcode -- 3 sum closest.

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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