Array/String permutation

Recursion/ArrayPermutationOne.java

@@ -0,0 +1,60 @@
+import java.util.*;
+
+class ArrayPermutationOne {
+
+    private void recurPermute(int[] nums, List<Integer> ds, List<List<Integer>> finalAnswer, boolean[] freq) {
+        
+        if (ds.size() == nums.length){
+            finalAnswer.add(new ArrayList<>(ds));
+            return;
+        }
+        
+        for (int i=0; i<nums.length; i++){
+            if(!freq[i]){
+                freq[i]=true;
+                ds.add(nums[i]);
+                recurPermute(nums, ds, finalAnswer, freq);
+                freq[i]=false;
+                ds.remove(ds.size()-1);
+            }
+        }
+    }
+
+    public List<List<Integer>> permute(int[] nums) {
+        List<List<Integer>> finalAnswer = new ArrayList<>();
+        List<Integer> ds = new ArrayList<>();
+        boolean[] freq = new boolean[nums.length];
+
+        recurPermute(nums, ds, finalAnswer, freq);
+        return finalAnswer;
+    }
+}
+
+public class Main {
+    public static void main(String[] args) {
+        Scanner sc = new Scanner(System.in);
+
+        // Input size
+        System.out.print("Enter number of elements: ");
+        int n = sc.nextInt();
+
+        int[] nums = new int[n];
+
+        // Input array elements
+        System.out.println("Enter elements:");
+        for (int i = 0; i < n; i++) {
+            nums[i] = sc.nextInt();
+        }
+
+        Solution obj = new Solution();
+        List<List<Integer>> result = obj.permute(nums);
+
+        // Print permutations
+        System.out.println("Permutations:");
+        for (List<Integer> perm : result) {
+            System.out.println(perm);
+        }
+
+        sc.close();
+    }
+}

Recursion/ArrayPermutationTwo.java

@@ -0,0 +1,62 @@
+import java.util.*;
+
+class ArrayPermutationTwo {
+
+    public void recurPermute(int index, int nums[], List<List<Integer>> finalAnswer){
+        if (index == nums.length){
+            ArrayList<Integer> ds = new ArrayList<>();
+            for(int i=0; i<nums.length; i++){
+                ds.add(nums[i]);
+            }
+            finalAnswer.add(new ArrayList<>(ds));
+            return;
+        }
+        
+        for (int i=index; i<nums.length; i++){
+            swap(index, i, nums);
+            recurPermute(index+1, nums, finalAnswer);
+            swap(index, i, nums);
+        }
+    }
+    
+    public void swap(int x, int y, int nums[]){
+        int temp = nums[x];
+        nums[x]=nums[y];
+        nums[y]=temp;
+    }
+
+    public List<List<Integer>> permute(int[] nums) {
+        List<List<Integer>> finalAnswer = new ArrayList<>();
+        recurPermute(0, nums, finalAnswer);
+        return finalAnswer;
+    }
+}
+
+public class Main {
+    public static void main(String[] args) {
+        Scanner sc = new Scanner(System.in);
+
+        // Input size
+        System.out.print("Enter number of elements: ");
+        int n = sc.nextInt();
+
+        int[] nums = new int[n];
+
+        // Input elements
+        System.out.println("Enter elements:");
+        for (int i = 0; i < n; i++) {
+            nums[i] = sc.nextInt();
+        }
+
+        Solution obj = new Solution();
+        List<List<Integer>> result = obj.permute(nums);
+
+        // Print permutations
+        System.out.println("Permutations:");
+        for (List<Integer> perm : result) {
+            System.out.println(perm);
+        }
+
+        sc.close();
+    }
+}