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Permutations.java

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package Recursion;

import java.util.ArrayList;

import java.util.List;

public class Permutations {

private static void permutation(String str,String ans) {

if(str.length() == 0) {

System.out.println(ans);

return;

}

char ch = str.charAt(0);

for(int i = 0;i<=ans.length();i++) {

String f = ans.substring(0, i);

String e = ans.substring(i,ans.length());

permutation(str.substring(1), f+ch+e);

}

private static ArrayList<String> permutationArrayList(String str,String ans) {

if(str.length() == 0) {

ArrayList<String> list = new ArrayList<>();

list.add(ans);

return list;

}

char ch = str.charAt(0);

ArrayList<String> arr = new ArrayList<>();

for(int i = 0;i<=ans.length();i++) {

String f = ans.substring(0, i);

String e = ans.substring(i,ans.length());

arr.addAll(permutationArrayList(str.substring(1), f+ch+e));

}

return arr;

}

private static int permutationCount(String str,String ans) {

if(str.length() == 0) {

// System.out.println(ans);

return 1;

}

int count = 0;

char ch = str.charAt(0);

for(int i = 0;i<=ans.length();i++) {

String f = ans.substring(0, i);

String e = ans.substring(i,ans.length());

count+=permutationCount(str.substring(1), f+ch+e);

}

return count;

}

// Array Permutation

static void permutationArray(int[] nums,List<List<Integer>> list,List<Integer> ans,int index) {

if(index == nums.length){

list.add(ans);

return;

}

for(int i = 0;i<=ans.size();i++){

List<Integer> temp = new ArrayList<>(ans) ;

temp.add(i,nums[index]);

permutationArray(nums,list,temp,index+1);

}

public static List<List<Integer>> Arraypermute(int[] nums) {

List<List<Integer>> list = new ArrayList<>();

permutationArray(nums,list,new ArrayList<Integer>(),0);

return list;

}

public static void main(String[] args) {

String str = "abc";

permutation(str,"");

System.out.println(permutationArrayList(str,""));

System.out.println(permutationCount("abcd",""));

System.out.println(Arraypermute(new int[] {1,2,3}));

}