2.Pair sum

#include <bits/stdc++.h> 
#include <bits/stdc++.h> 
vector<vector<int>> pairSum(vector<int> &arr, int s){
   // Write your code here.
    vector <vector <int>  > ans ; 
    map <int,int> m ;
  // sort(arr.begin(),arr.end());
   for(int i = 0 ; i < arr.size();i++)
   {
       
      
      if(m.count(s - arr[i]) > 0 )
      {
          int k = m[s - arr[i]] ;
         // cout << k << arr[i] << endl ;
          for(int j = 0 ; j <  k; j++)         {
              vector <int> res ; 
              if(arr[i] < s - arr[i])
              {
              res.push_back(arr[i]) ;
              res.push_back(s - arr[i]) ;
              }
              else
              {
                  res.push_back(s - arr[i]) ;
                  res.push_back(arr[i]) ;
              }
                ans.push_back(res) ;
            
              
          }
      }
        m[arr[i]]++ ;
   }
    sort(ans.begin(), ans.end()) ; 
    return ans ; 
}