LC#46, clean code-returns all permutations of given array of numbers

Author: NirmalSilwal

Leetcode/medium/Permutations46.java

@@ -5,33 +5,67 @@
 
 public class Permutations46 {
 
-	public static List<List<Integer>> permute(int[] nums) {
+	public static List<List<Integer>> permute1(int[] nums) {
 		List<List<Integer>> list = new ArrayList<>();
 		ArrayList<Integer> templist = new ArrayList<>();
-		
-		permute(nums, templist, list);
-		
+
+		permute1(nums, templist, list);
+
 		return list;
 	}
 
-	private static void permute(int[] nums, List<Integer> temp, List<List<Integer>> list) {
-		
+	private static void permute1(int[] nums, List<Integer> temp, List<List<Integer>> list) {
+
 		if (temp.size() == nums.length) {
 			list.add(new ArrayList<>(temp));
 			return;
 		}
-		
+
 		for (int i = 0; i < nums.length; i++) {
 			if (temp.contains(nums[i]))
 				continue;
 			temp.add(nums[i]);
-			
-			permute(nums, temp, list);
-			
+
+			permute1(nums, temp, list);
 			temp.remove(temp.size() - 1);
 		}
 	}
 
+	// O(N!) Time - using visited mark
+	public static List<List<Integer>> permute(int[] nums) {
+
+		List<List<Integer>> result = new ArrayList<>();
+		boolean[] visited = new boolean[nums.length];
+
+		backtrack(nums, visited, new ArrayList<Integer>(), result);
+
+		return result;
+	}
+
+	private static void backtrack(int[] nums, boolean[] visited, ArrayList<Integer> permutations,
+			List<List<Integer>> result) {
+
+		if (permutations.size() == nums.length) {
+			result.add(new ArrayList<>(permutations)); // deep-copy
+			return;
+		}
+
+		for (int i = 0; i < nums.length; i++) {
+
+			if (visited[i] == true)
+				continue;
+
+			permutations.add(nums[i]);
+			visited[i] = true;
+
+			backtrack(nums, visited, permutations, result);
+
+			permutations.remove(permutations.size() - 1); // remove recently
+															// visited
+			visited[i] = false;
+		}
+	}
+
 	public static void main(String[] args) {
 		int[] nums = { 1, 2, 3 };
 		System.out.println(permute(nums));