Function checks if the boundary of the square consists of 0 's
bool isSquareOfZeroes ( vector < vector < int > > & matrix , int r1 , int c1 , int r2 , int c2 ) { for ( int row = r1 ; row < r2 + 1 ; row ++ ) { if ( matrix [ row ] [ c1 ] != 0 matrix [ row ] [ c2 ] != 0 ) return false ; } for ( int col = c1 ; col < c2 + 1 ; col ++ ) { if ( matrix [ r1 ] [ col ] != 0 matrix [ r2 ] [ col ] != 0 ) return false ; } return true ; }