Initializing right and down array .
for ( let i = 0 ; i < n ; i ++ ) { for ( let j = 0 ; j < m ; j ++ ) { right [ i ] [ j ] = Math . max ( 0 , ( j + 1 == m ? 0 : right [ i ] [ j + 1 ] ) ) + arr [ i ] [ j ] ; down [ i ] [ j ] = Math . max ( 0 , ( i + 1 == n ? 0 : down [ i + 1 ] [ j ] ) ) + arr [ i ] [ j ] ; } }