Driver code
public static void main ( String [ ] args ) { char [ ] str = "4321" . toCharArray ( ) ; if ( prevPermutation ( str ) ) { System . out . println ( " Previous ▁ permutation ▁ is ▁ " + String . valueOf ( str ) ) ; } else { System . out . println ( " Previous ▁ permutation " + " doesn ' t ▁ exist " ) ; } } }