3Sum Closest Solution: O(N^2)

3sumclosest.cpp

class Solution {
public:
    int threeSumClosest(vector<int>& nums, int target) {
        if (nums.size() < 3)
            return 0;
        int ans = nums[0] + nums[1] + nums[2];
        sort(nums.begin(), nums.end());
        for (int i = 0, n = nums.size(); i < n; ++i) {
            int lo = i + 1, hi = n - 1;
            while (lo < hi) {
                int sum = nums[i] + nums[lo] + nums[hi];
                if (sum == target)
                    return target;
                
                if (abs(sum - target) < abs(ans - target))
                    ans = sum;
                
                if (sum < target)   ++lo;
                else                --hi;
            }
        }
        return ans;
    }
};