3Sum(cpp,leetcode)

Given an array nums of n integers, are there elements a, b, c in nums such that a + b + c = 0? Find all unique triplets in the array which gives the sum of zero.

Notice that the solution set must not contain duplicate triplets.

Example 1:

Input: nums = [-1,0,1,2,-1,-4]
Output: [[-1,-1,2],[-1,0,1]] 

================================================================================

class Solution {
public:
    vector<vector<int>> threeSum(vector<int>& a) 
    { 
        
    
        sort(a.begin(),a.end());
        int left,right;
        vector<vector<int>>v;
        
        if(a.size()<3)
        {
            
            return v;
        }
        
        
        // left=1;
        // right=a.size()-1;
        
        for(int i=0;i<a.size()-2;i++)
        {
            int t=a[i];
            left=i+1;
            right=a.size()-1;
            if(i>0 && a[i]==a[i-1])
                continue;
            
            while(left<right)
            {
                if(t+a[left]+a[right]==0)
                {
                    vector<int>q={t,a[left],a[right]};
                    v.push_back(q);
                   
                    
                    while(left<right && a[left]==a[left+1])
                    {
                        left++;
                    }
                    while(left<right && a[right]==a[right-1])
                    {
                        right--;
                    }
                    left++;
                    right--;
                    
                }
                
                else if(t+a[left]+a[right]>0)
                {
                    right--;
                }
                else if(t+a[left]+a[right]<0)
                {
                    left++;
                    
                }
                    
                
            }
            
            
        }
        return v;
        
    }
};