[gcj] CodeJam 2020 Round 1B - 3.JoinTheRanks - WA for my submission

[Atif Hussain]

Hi, 
For Google CodeJam 2020 Round 1B - 3.JoinTheRanks - below was my C++ 
submission, which gave WA for hidden inputs. 
https://codingcompetitions.withgoogle.com/codejam/round/000000000019fef2/00000000002d5b64
Please help identify my error - in code, or input where it fails. 


#include <bits/stdc++.h>
using namespace std;

int main()
{
    int testcases; cin >> testcases;    
    for (int t = 1; t <= testcases; t++) {
        int R, S; cin >> R >> S;

        vector<pair<int, int>> deck(R*S);
        for (int j = 0; j < S; j++)
            for (int i = 0; i < R; i++)
                deck[i + R * j].first = i + 1,
                deck[i + R * j].second = j + 1;

        vector<pair<int, int>> moves;
        int till, from;
        for (till = R * S - 1; till >= 0; till--) {
            int toR = (till / S) + 1;
            if (deck[till].first==toR) continue;
            
            for (from = till - 1; deck[from].first != toR; from--); 

            // deck[from].first = toR != deck[till].first
            from++; till++;
            moves.push_back(make_pair(from, till-from));
            vector<pair<int, int>> A(deck.begin(), deck.begin() + from);
            vector<pair<int, int>> B(deck.begin()+from, deck.begin() + 
till);
            deck.erase(deck.begin() + from, deck.begin() + till);
            deck.insert(deck.begin(), B.begin(), B.end());
        }

        cout << "Case #" << t << ": " << moves.size() << endl;
        for (int i = 0; i < moves.size(); i++)
            cout << moves[i].first << " " << moves[i].second << endl;
    }
    return 0;
}

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