Решение задачи Фермер с Acmp

#include <iostream>
#include <vector>
#include <fstream>
using namespace std;
 
int main()
{
    ifstream fin("input.txt");
    ofstream fout("output.txt");
    unsigned n;
    char tch;
    fin >> n;
    vector< vector< unsigned short > > m;
    vector< unsigned short > t;
    unsigned maxK = 0;
 
    for(unsigned i = 0; i < n; ++i) {
        t.clear();
        int k = 0;
        for(unsigned j = 0; j < n; ++j) {
            fin >> tch;
            t.push_back(tch - 48);
            if(tch - 48)
                maxK = 1;
        }
        m.push_back(t);
    }
 
 
    for(int i = n - 2; i >= 0; --i) {
        for(int j = n - 2; j >= 0; --j) {
            int lmin = min(m.at(i).at(j + 1),
                           min(m.at(i + 1).at(j), m.at(i + 1).at(j + 1)));
            if(m.at(i).at(j) && lmin) {
                m.at(i).at(j) = lmin + 1;
                if(maxK < m.at(i).at(j))
                    maxK = m.at(i).at(j);
            }
        }
    }
 
    fout << maxK * maxK;
 
    return 0;
}