Created Permutations.java from Leetcode

Leetcode 46 : https://leetcode.com/problems/permutations/

Author: Sanatan-Shrivastava

leetcode/Java/Permutations.java

@@ -0,0 +1,56 @@
+package BackTracking;
+import java.util.*;
+
+    /*
+    Given a collection of distinct integers, return all possible permutations.
+
+    Example:
+
+    Input: [1,2,3]
+    Output:
+    [
+    [1,2,3],
+    [1,3,2],
+    [2,1,3],
+    [2,3,1],
+    [3,1,2],
+    [3,2,1]
+    ]
+    */
+public class Permutations {
+    class Solution {
+        public List<List<Integer>> permute(int[] nums) {
+            List<List<Integer>> permutations = new ArrayList<>();
+            boolean[] seen = new boolean[nums.length];
+            if(nums == null || nums.length == 0) {
+                return permutations;
+            }
+            findPermutations(nums, permutations, new ArrayList<>(), seen);
+            return permutations;
+        }
+    
+        private void findPermutations (int[] nums, List<List<Integer>> permutations, List<Integer> current, boolean[] seen) {
+            if(current.size() > nums.length) {
+                return;
+            }
+        
+            if(current.size() == nums.length) {
+                permutations.add(new ArrayList<>(current));
+                return;
+            }
+        
+            for(int i = 0; i < nums.length; i++) {
+                if(seen[i] == true) {
+                    continue;
+                }
+                current.add(nums[i]);
+                seen[i] = true;
+                findPermutations(nums, permutations, current, seen);
+                current.remove(current.size() - 1);
+                seen[i] = false;
+            }
+        
+            return;
+        }
+    } 
+}