( m , n ) can be reached either through ( m - 1 , n ) or through ( m , n - 1 )
dp [ m , n , k ] = pathCountDPRecDP ( mat , m - 1 , n , k - mat [ m , n ] ) + pathCountDPRecDP ( mat , m , n - 1 , k - mat [ m , n ] ) ; return dp [ m , n , k ] ; }