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【LeetCode】3Sum Closest

3Sum Closest

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).

 

先确定第一个数字,然后用双指针遍历,不断更新最接近的值。

复杂度O(n2)

class Solution {public:    int threeSumClosest(vector<int> &num, int target) {        int gap = INT_MAX;        int sum = 0;        sort(num.begin(), num.end());        for(int i = 0; i < num.size()-2; i ++)        {            int j = i+1;            int k = num.size()-1;            while(j < k)            {                int tmp = num[i]+num[j]+num[k];                if(abs(tmp-target) < gap)                {                    gap = abs(tmp-target);                    sum = tmp;                }                if(tmp == target)                    return target;                else if(tmp < target)                    j ++;                else                    k --;            }        }        return sum;    }};

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【LeetCode】3Sum Closest