【Leetcode】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).

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

与上题3Sum类似，先排序，然后以一个元素为准，两边夹逼，逐个求三个元素的和，找到与目标相等的了可以直接返回，对于重复元素可以只找一次。