permutation with duplicate

Recursion/PermutationWithDuplicate.java

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+import java.util.*;
+
+//leetcode 47 permutation 1, 2
+public class PermutationWithDuplicate {
+
+
+    public static List<List<Integer>> permuteUnique(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;
+        }
+       Set<Integer> m = new HashSet<>();
+        for (int i = numsIdx; i < nums.length; i++) {
+            if (!m.contains(nums[i])) {
+                swap2(nums, i, numsIdx);
+                slate.add(nums[numsIdx]);
+                m.add(nums[numsIdx]);
+                permuteHelper(nums, numsIdx+1, slate, result);
+                swap2(nums, i, numsIdx);
+                slate.remove(slate.size() - 1);
+            }
+        }
+    }
+
+        public static void swap2(int[] nums, int v1, int v2){
+            int temp = nums[v2];
+            nums[v2] = nums[v1];
+            nums[v1] = temp;
+        }
+
+        public static void main (String[]args){
+            int[] a = {1, 1, 2,2};
+            List<List<Integer>> result = permuteUnique(a);
+            System.out.println(result);
+
+        }
+    }
+