Doubt regarding Tricky permutations problem

#1

Only 1 test case is failing due to TLE . Can you help me , where should I optimize my code ?

import java.util.*;
public class Main {
public static void main(String args[]) {

	Scanner scan = new Scanner(System.in) ;
	String str = scan.next() ;
	ArrayList<String> ans = new ArrayList<>() ;
	permutations(str,"",ans) ;
	Collections.sort(ans) ;
	for(String val : ans){
		System.out.println(val) ;
	}

}

public static void permutations(String str , String ans , ArrayList<String> al){

	if(str.length() == 1){
		String res = ans+str;
		if(!al.contains(res)){
			al.add(res) ;
		}
		return ;
	}

	for(int i = 0 ; i < str.length() ; i ++){
		permutations(str.substring(0,i)+str.substring(i+1) , ans+str.charAt(i) , al) ;
	}
}

}

#2

@Lalit2142,
Instead of using arraylist use an array and sort the chars in the array before calling the permutations function.

al.contains(): the contains method in arraylist has a worst case time complexity of O(N). reduce that.

#3

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