text: Consider all possible pairs mat [ a ] [ b ] and mat [ d ] [ e ]
code: for ( int a = 0 ; a < N - 1 ; a ++ ) for ( int b = 0 ; b < N - 1 ; b ++ ) for ( int d = a + 1 ; d < N ; d ++ ) for ( int e = b + 1 ; e < N ; e ++ ) if ( maxValue < ( mat [ d ] [ e ] - mat [ a ] [ b ] ) ) maxValue = mat [ d ] [ e ] - mat [ a ] [ b ] ; return maxValue ; }