3Sum.cpp

#include <iostream>
#include <vector>
#include <algorithm>
using namespace std;

class Solution
{
public:
    //[nums[i], nums[j], nums[k]] such that i != j, i != k, and j != k, and nums[i] + nums[j] + nums[k] == 0.
    vector<vector<int>> threeSum(vector<int> &nums)
    {
        vector<int> triplets;
        vector<vector<int>> result;
        sort(nums.begin(), nums.end());

        for (int i = 0; i < nums.size(); ++i)
        {
            if (i > 0 && nums[i] == nums[i - 1])
            {
                continue;
            }
            int left = i + 1;
            int right = nums.size() - 1;
            while (left < right)
            {
                int sum = nums[i] + nums[left] + nums[right];
                if (sum == 0)
                {
                    result.push_back({nums[i], nums[left], nums[right]});
                    left++;
                    right--;

                    while (left < right && nums[left] == nums[left - 1])
                    {
                        left++;
                    }
                    while (left < right && nums[right] == nums[right + 1])
                    {
                        right--;
                    }
                }
                else if (sum < 0)
                {
                    left++;
                }
                else
                {
                    right--;
                }
            }
        }
        return result;
    }
};