Count strings with consecutive 1 's | Returns count of n length binary strings with consecutive 1 's ; Count binary strings without consecutive 1 's.  See the approach discussed on be  ( http:goo.gl/p8A3sW ) ; Subtract a [ n - 1 ] + b [ n - 1 ] from 2 ^ n ; Driver Code
function countStrings ( n ) { let a = [ ] , b = [ ] ; a [ 0 ] = b [ 0 ] = 1 ; for ( let i = 1 ; i < n ; i ++ ) { a [ i ] = a [ i - 1 ] + b [ i - 1 ] ; b [ i ] = a [ i - 1 ] ; } return ( 1 << n ) - a [ n - 1 ] - b [ n - 1 ] ; } document . write ( countStrings ( 5 ) ) ;