C++ 3sum complexity

Question

I was trying to solve the 3 sum problem in cpp.

Given an array S of n integers, are there elements a, b, c in S such that a + b + c = 0? Find all unique triplets in the

Answer 1

Here is my solution that finds all unique triplets in O(n^2) run-time.

class Solution {

    public: vector> threeSum(vector& nums) {    
        int len = nums.size();

        if(len<3) return {};

        sort(nums.begin(), nums.end());

        vector> retVector;

        int target, begin, end;    

        int i=0;
        while(i < len - 2)                  
        {
            int dup;    //  to find duplicates entries

            target = -nums[i];

            begin = i + 1; end = len - 1;

            while (begin < end)
                {
                    if (nums[begin] + nums[end] < target) begin++;                  

                    else if (nums[begin] + nums[end] > target) end--;                   

                        else
                        {

                            retVector.push_back({nums[i], nums[begin], nums[end]}); 

                            //  its time to remove duplicates

                            dup=nums[begin];    

                            do begin++; while(nums[begin] == dup);   //  removing from front

                            dup=nums[end]; 

                            do end--; while(nums[end] == dup);     //  removing from back                                                        
                        }                                                                                               
                }

            dup=nums[i];

            do i++; while(nums[i] == dup) ;     //  removing all ertries same as nums[i]            

        }                                      
        return retVector;
    }     
};