Character recognition

#include<bits/stdc++.h>
using namespace std;
int main()
{
	int c,n,m;
	cin>>m>>n>>c;
	int matrix[c+1][n+1][m+1]; // x,y,z such that xth 2D matrix represnt xth character
	for(int i=1;i<=c;i++)
	{
        for(int j=1;j<=m;j++)
        {
            for(int k=1;k<=n;k++)
            {
                cin>>matrix[i][j][k];
            }
        }
	}
	bool compared[100][100] = {0};
	vector<set<pair<int,int>>> V;
	for(int i=1;i<=c;i++)
	{
        for(int j=1;j<=c;j++)
        {
            if(i!=j && !compared[i][j] && !compared[j][i])
            {
                set<pair<int,int>> S;
                compared[i][j] = compared[j][i] = 1;
                for(int x=1;x<=m;x++)
                {
                    for(int y=1;y<=n;y++)
                    {
                        if(matrix[i][x][y] != matrix[j][x][y])
                        {
                            S.insert(make_pair(x,y));
                        }
                    }
                }
                V.push_back(S);
            }
        }
	}
	map<pair<int,int>,int> M; // for keeping record that a point x,y exists in how many comparisions
	bool included[100];
	memset(included,0,sizeof(included));
	bool done = 0;
	int ans = 0;
	while(!done)
	{
        for(int i=0;i<V.size();i++)
        {
            if(!included[i])
            for(auto it = V[i].begin();it!=V[i].end();it++)
            {
                M[*it]++;
            }
        }
        int maxi = 0;
        pair<int,int> P;
        for(auto it = M.begin() ; it!=M.end() ; it++)
        {
            if(it->second > maxi)
            {
                P = it->first;
                maxi = it->second;
            }
        }
        for(int i=0;i<V.size();i++)
        {
            if(!included[i] && V[i].find(P)!=V[i].end())
            {
                included[i] = 1;
                V[i].erase(P);
            }
        }
        ans++;
        int i;
        for(i=0;i<V.size();i++)
        {
            if(!included[i])
            {
                break;
            }
        }
        if(i==V.size())
        {
            done = 1;
        }
        M.clear();
    }
    cout<<ans<<endl;
	return 0;
}