permutation without duplicate

Recursion/Permutation.java

@@ -0,0 +1,43 @@
+import java.util.ArrayList;
+import java.util.List;
+//46 leetcode
+//sc = n + n.n! + n *n!
+//TC = n * n!
+public class Permutation {
+
+    public static List<List<Integer>> permutation(int[] nums) {
+        List<Integer> slate = new ArrayList<>(nums.length);
+        List<List<Integer>> result = new ArrayList<>();
+        permuteHelper(nums, 0, slate, result);
+        return result;
+    }
+
+    public static void permuteHelper(int[] nums, int numsIdx, List<Integer> slate, List<List<Integer>> result) {
+        if (nums.length == numsIdx) {
+            result.add(new ArrayList<>(slate));
+            return;
+        }
+        for (int i = numsIdx; i < nums.length; i++) {
+            swap(nums, i, numsIdx);
+            slate.add(nums[numsIdx]);
+            permuteHelper(nums, numsIdx + 1, slate, result);
+            swap(nums, i, numsIdx);
+            slate.remove(slate.size() - 1);
+        }
+    }
+
+    public static void swap(int[] nums, int v1, int v2) {
+        int temp = nums[v2];
+        nums[v2]= nums[v1];
+        nums[v1] = temp;
+    }
+
+    public static void main(String[] args) {
+        int[] nums = {1, 2, 3};
+        List<List<Integer>> result = new ArrayList<>();
+        result = permutation(nums);
+        System.out.println(result);
+
+    }
+
+}