3Sum Closest -- LeetCode

3Sum Closest

(原題鏈接：點擊打開鏈接)

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).

Solution：

class Solution {
public:
    int threeSumClosest(vector<int>& nums, int target) {
        if(nums.size() < 3) return target;
        sort(nums.begin(), nums.end());
        int closest = nums[0] + nums[1] + nums[2];
        int min = abs(closest - target);
        for (int a = 0; a < nums.size() - 2; a++)
        {
            int b = a + 1;
            int k = nums.size() - 1;
            while(b < k)
            {
                int sum = nums[a] + nums[b] + nums[k];
                int sub = abs(sum - target);
                if (sub < min)
                {
                    closest = sum;
                    min = sub;
                }
                if (sum > target)
                {
                    while(nums[--k] == nums[k+1]) ;
                }
                else if (sum < target)
                {
                    while(nums[++b] == nums[b-1]) ;
                }
                else
                {
                    return target;
                }
            }
        }
        return closest;
    }
};