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

3sum.cpp

#include <iostream>
#include <vector>

using namespace std;

class Solution {
public:
    vector<vector<int>> threeSum(vector<int> nums)
    {
        if (nums.size() < 3) return{};
        sort(nums.begin(), nums.end());
        vector<vector<int>> output;
        for (size_t i = 0; i < nums.size() - 2; i++)
        {
            size_t front = i + 1;
            size_t back = nums.size() - 1;
            int sum = 0 - nums[i];
            while (front < back)
            {
                if (nums[front] + nums[back] == sum)
                {
                    output.push_back({ nums[i], nums[front], nums[back] });
                    while ((front < back) && nums[front] == nums[front + 1]) front++;
                    while ((back < front) && nums[front] == nums[back - 1]) back--;
                    front++; back--;
                }
                else if (nums[front] + nums[back] < sum) front++;
                else back--;
            }
            while ((i < nums.size() - 2) && nums[i] == nums[i + 1]) i++;
        }


        return output;
    }
};

int main()
{
    Solution a;
    auto b = a.threeSum({ 1, -1, -1, 0 });

    return 0;
}