RE

关于我这串代码是RE。
为什么啊?想来想去也没找到是哪里的问题。
求各位大佬帮我看一下是哪里出现了格式的错误等等。
崩溃了

#include <iostream>
#include <vector>
#include <algorithm>
using namespace std; 
int main() {
    long long  n, m;
    cin >> n >> m;
    vector<vector<int>> balls(n, vector<int>(m));
        for (int i = 0; i < n; i++) {
            for (int j = 0; j < m; j++) {
                cin >> balls[i][j];
            }
        }
    vector<pair<int, int>> moves; 

    for (int color = 0; color < m; color++) {
        vector<pair<int , int>> count; 
        for (int i = 0; i <= n; i++) {
            int cnt = 0;
                for (int j = 0; j < m; j++) {
                    if (balls[i][j] == color) {
                            cnt++;
    }
    }
    count.push_back({cnt, i});
    } 
        sort(count.begin(), count.end()); 
        
        for (int i = 0; i < n; i++) {
            if (count[i].first == 0) break;
            long long from = count[i].second;
            long long to = count[n].second;
            moves.push_back({from + 1, to + 1}); 
            balls[to][count[n].first - 1] = balls[from][count[i].first - 1];
            balls[from][count[i].first - 1] = 0; 
        }
    }
    cout << moves.size() << endl;
    for (auto move : moves) {
        cout << move.first << " " << move.second << endl;
    }
    return 0;
}

求帮助