How to print maximum number of A 's using given four keys | This function returns the optimal length string for N keystrokes ; The optimal string length is N when N is smaller than 7 ; An array to store result of subproblems ; To pick a breakpoint ; Initializing the optimal lengths array for uptil 6 input strokes . ; Solve all subproblems in bottom - up manner ; for any keystroke n , we will need to choose between : - 1. pressing Ctrl - V once after copying the A ' s ▁ obtained ▁ by ▁ n - 3 ▁ keystrokes . ▁ ▁ 2 . ▁ pressing ▁ Ctrl - V ▁ twice ▁ after ▁ ▁ copying ▁ the ▁ A ' s obtained by n - 4 keystrokes . 3. pressing Ctrl - V thrice after copying the A 's  obtained by n-5 keystrokes. ; Driver program ; for the rest of the array we will rely on the previous entries to compute new ones
function findoptimal ( N ) { if ( N <= 6 ) return N ; let screen = [ ] ; let b ; let n ; for ( n = 1 ; n <= 6 ; n ++ ) screen [ n - 1 ] = n ; for ( n = 7 ; n <= N ; n ++ ) { screen [ n - 1 ] = Math . max ( 2 * screen [ n - 4 ] , Math . max ( 3 * screen [ n - 5 ] , 4 * screen [ n - 6 ] ) ) ; } return screen [ N - 1 ] ; } let N ; for ( N = 1 ; N <= 20 ; N ++ ) document . write ( " " + N + " " + findoptimal ( N ) + " " ) ;