Наибольшая общая подпоследовательность

vector<pair<int,int> > getNOP(string& s1, string& s2){
    vector< vector<int> >dp(105,vector<int>(105,0));
    vector< vector<pair<int ,int> > > prev(105,vector<pair<int ,int> >(105));

    for(int i=1;i<=s1.size();++i){
        for(int j=1;j<=s2.size();++j){
            if(s1[i-1] == s2[j-1]){
                dp[i][j] = dp[i-1][j-1]+1;
                prev[i][j] = {i-1,j-1};
            }else if(dp[i-1][j] > dp[i][j-1]){
                dp[i][j] = dp[i-1][j];
                prev[i][j] = {i-1,j};
            }else{
                dp[i][j] = dp[i][j-1];
                prev[i][j] = {i,j-1};
            }
        }
    }

    int indexI = s1.size();
    int indexJ = s2.size();
    cout<<dp[indexI][indexJ]<<endl;
    vector<pair<int,int> >ans;

    while(indexI > 0 || indexJ > 0){

        if(prev[indexI][indexJ].first == indexI-1 && prev[indexI][indexJ].second  ==  indexJ-1  )   {
           ans.push_back({indexI,indexJ});
        }
        int newI = prev[indexI][indexJ].first;
        int newJ = prev[indexI][indexJ].second;
        indexI = newI;
        indexJ =newJ;
    }
    return ans;
}