3SumClosest.cpp

// Given an integer array nums of length n and an integer target, find three integers in nums such that the sum is closest to target.

// Return the sum of the three integers.

// You may assume that each input would have exactly one solution.

// https://leetcode.com/problems/3sum-closest/

// Example 1:

// Input: nums = [-1,2,1,-4], target = 1
// Output: 2
// Explanation: The sum that is closest to the target is 2. (-1 + 2 + 1 = 2).



int threeSumClosest(vector<int>& nums, int target) {
    if(nums.size() < 3) return 0;
    int closest = nums[0]+nums[1]+nums[2];
    sort(nums.begin(), nums.end());
    for(int first = 0 ; first < nums.size()-2 ; ++first) {
        if(first > 0 && nums[first] == nums[first-1]) continue;
        int second = first+1;
        int third = nums.size()-1;            
        while(second < third) {
            int curSum = nums[first]+nums[second]+nums[third];
            if(curSum == target) return curSum;
            if(abs(target-curSum)<abs(target-closest)) {
                closest = curSum;
            }
            if(curSum > target) {
                --third;
            } else {
                ++second;
            }
        }
    }
    return closest;
}