k - starting row index m - ending row index l - starting column index n - ending column index i - iterator
int i , k = 0 , l = 0 ; int m = a . size ( ) , n = a [ 0 ] . size ( ) ; int n_i , n_k = 0 , n_l = 0 , n_m = m , n_n = n ; while ( k < m && l < n ) {