◻️16. 3Sum Closest (medium)

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.

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).

Example 2:

Input: nums = [0,0,0], target = 1
Output: 0
Explanation: The sum that is closest to the target is 0. (0 + 0 + 0 = 0).

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Solutions

Optimised

Runtime 17 ms Memory 13.01 MB

```cpp
class Solution {
public:
    int threeSumClosest(vector<int>& nums, int target) {
        long long int n=nums.size();
        if(n<3) return {};
        ranges::sort(nums);
        long long int closest=INT_MAX;
        for(int i=0; i+2<nums.size(); ++i){
            if(i>0 && nums[i]==nums[i-1]){continue;}
            int l=i+1, r=n-1;
            while(l<r){
                int sum = nums[i]+nums[l]+nums[r];
                if(sum==target){
                    return(sum);
                }
                else if(sum>target){
                    --r;
                }
                else{
                    ++l;
                }
                if(abs(sum-target)<abs(closest-target)) closest = sum;
            }
        }
        return closest;
    }
};
```