[Leetcode C++] 3Sum Closest

Problem

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) {
int minDiff = INT_MAX;
if(nums.size()<3) return minDiff;
sort(nums.begin(), nums.end());
for(int i=0; i<nums.size()-2; i++){
int left = i+1;
int right = nums.size()-1;
while(left < right){
int currDiff = nums[i] + nums[left] + nums[right] - target;

//update diff
if(abs(minDiff) > abs(currDiff))
minDiff = currDiff;

//special case
if(currDiff == 0) break;
else if (currDiff < 0) left++;
else right--;
}
}
return target + minDiff;
}
};
```

Analysis

This problem is similar to 3Sum problemĀ http://mytechroad.com/leetcode-c-3sum/

Time complexity: O(n^2)