[LeetCode]3Sum Closest

题目描述:(链接)

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).

解题思路:

排序，左右夹逼！

class Solution {
public:
    int threeSumClosest(vector<int>& nums, int target) {
        int result = 0;
        if (nums.size() < 3) { return result; }
        
        int min = INT_MAX;
        sort(nums.begin(), nums.end());
        
        auto last = nums.end();
        for (auto i = nums.begin(); i != prev(last, 2); ++i) {
            auto j = i + 1;
            auto k = last - 1;
            
            while (j < k) {
                int sum = *i + *j + *k;
                int gap = abs(sum - target);
                if (gap < min) {
                    result = sum;
                    min = gap;
                }
                if (sum < target) { 
                    ++j ;
                } else {
                    --k;
                }
            }
        }
        
        return result;
    }
};