LeetCode 16 - 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).

My Code

class Solution {public:    int threeSumClosest(vector<int>& nums, int target) {        int size = nums.size();        int result = 0;        sort(nums.begin(), nums.end());        int min_dis = INT_MAX;        for (int i = 0; i < size - 2; i++)        {            // Omit duplicate numbers            if (i > 0 && nums[i] == nums[i-1])                continue;            int last_idx = size - 1;            while (last_idx > i + 1 && nums[i] + nums[i+1] + nums[last_idx] >= target)                last_idx--;            // All subsequent sets are increasing and not smaller than target            if (last_idx == i + 1)            {                int sum = nums[i] + nums[i+1] + nums[i+2];                int cur_dis = abs(sum - target);                if (min_dis > cur_dis)                {                    min_dis = cur_dis;                    result = sum;                }                break;            }            int n = last_idx;            for (int m = i + 1; m < size - 1; m++)            {                if (m > i + 1 && nums[m] == nums[m-1])                    continue;                // n moves left from last_idx                while (n > m && nums[i] + nums[m] + nums[n] >= target)                    n--;                int small_sum = nums[i] + nums[m] + nums[n], large_sum = small_sum;                int nn = n + 1;                while (nn < size && nums[n] == nums[nn])                    nn++;                if (nn < size)                    large_sum = nums[i] + nums[m] + nums[nn];                int large_sum_dis = abs(large_sum - target), small_sum_dis = abs(small_sum - target);                if (large_sum_dis < small_sum_dis)                {                    if (min_dis > large_sum_dis)                    {                        result = large_sum;                        min_dis = large_sum_dis;                    }                }                else                {                    if (min_dis > small_sum_dis)                    {                        result = small_sum;                        min_dis = small_sum_dis;                    }                }                if (min_dis == 0)                    return result;                // All subsequent sets are increasing and not smaller than target                if (nums[i] + nums[m] + nums[n] > target)                    break;            }        }        return result;    }};

Runtime:16 ms