Find the number of integers from 1 to n which contains digits 0 ' s ▁ and ▁ 1' s only | Function to find the number of integers from 1 to n which contains 0 ' s ▁ and ▁ 1' s only ; If number is greater than n ; otherwise add count this number and call two functions ; Driver code
< ? php function countNumbers ( $ x , $ n ) { if ( $ x > $ n ) return 0 ; return 1 + countNumbers ( $ x * 10 , $ n ) + countNumbers ( $ x * 10 + 1 , $ n ) ; } $ n = 120 ; echo ( countNumbers ( 1 , $ n ) ) ; ? >