151.cpp

/*
    Solution for the problem 151 of aceptaelreto.com

    - Es matriz identidad - 

    Copyright (C) 2018 hnko
    This program is free software: you can redistribute it and/or modify
    it under the terms of the GNU General Public License as published by
    the Free Software Foundation, either version 3 of the License, or
    (at your option) any later version.

    This program is distributed in the hope that it will be useful,
    but WITHOUT ANY WARRANTY; without even the implied warranty of
    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
    GNU General Public License for more details.

    You should have received a copy of the GNU General Public License
    along with this program.  If not, see <http://www.gnu.org/licenses/>.
*/
#include <iostream>

using namespace std;
int matrix[50][50], n;

/* look if it is identity matrix */
bool isIdentity(){
    for(int i=0; i<n; i++){
        for(int j=0; j<n; j++){
            if(i == j) {
                if (matrix[i][j] != 1) return false;
            }else if(matrix[i][j] != 0) return false;
        }
    }
    return true;
}

int main(){

    while (true){
        scanf("%d", &n); if(n == 0) return 0;

        /* scan the matrix*/
        for(int i=0; i<n; i++){
            for(int j=0; j<n; j++){
                scanf("%d", &matrix[i][j]);
            }
        }
        /* give the result */
        printf(isIdentity() ? "SI\n" : "NO\n");
    }
}