solves permutations ii

Author: anishLearnsToCode

README.md

@@ -47,6 +47,7 @@
 |  43  | [Multiply Strings](https://leetcode.com/problems/multiply-strings)                                                                                        |                                                                 [![Java](assets/java.png)](src/MultiplyStrings.java)                                                                 |                                                                                                                                   |
 |  45  | [Jump Game II](https://leetcode.com/problems/jump-game-ii)                                                                                                |                                                                   [![Java](assets/java.png)](src/JumpGameII.java)                                                                    |                                                                                                                                   |
 |  46  | [Permutations](https://leetcode.com/problems/permutations)                                                                                                |                                                                  [![Java](assets/java.png)](src/Permutations.java)                                                                   |                                                                                                                                   |
+|  47  | [Permutations II](https://leetcode.com/problems/permutations-ii)                                                                                          |                                                                 [![Java](assets/java.png)](src/PermutationsII.java)                                                                  |                                                                                                                                   |
 |  53  | [Maximum SubArray](https://leetcode.com/problems/maximum-subarray)                                                                                        |                                 [![Java](assets/java.png)](src/MaximumSubArray.java) [![Python](assets/python.png)](python/maximum_sum_subarray.py)                                  |                                                                                                                                   |
 |  55  | [Jump Game](https://leetcode.com/problems/jump-game)                                                                                                      |                                                                    [![Java](assets/java.png)](src/JumpGame.java)                                                                     |                                                                                                                                   |
 |  58  | [Length of Last Word](https://leetcode.com/problems/length-of-last-word)                                                                                  |                                 [![Java](assets/java.png)](src/LengthOfLastWord.java) [![Python](assets/python.png)](python/length_of_last_word.py)                                  |                                                                                                                                   |

src/PermutationsII.java

@@ -0,0 +1,42 @@
+// https://leetcode.com/problems/permutations-ii
+// T: O(n * n!)
+// S: O(n * n!)
+
+import java.util.ArrayList;
+import java.util.HashMap;
+import java.util.LinkedList;
+import java.util.List;
+import java.util.Map;
+
+public class PermutationsII {
+    public List<List<Integer>> permuteUnique(int[] nums) {
+        final Map<Integer, Integer> frequencies = getFrequencies(nums);
+        final List<List<Integer>> result = new ArrayList<>();
+        permuteUnique(nums, result, frequencies, new LinkedList<>());
+        return result;
+    }
+
+    private void permuteUnique(int[] array, List<List<Integer>> result, Map<Integer, Integer> frequencies, LinkedList<Integer> current) {
+        if (current.size() == array.length) {
+            result.add(new ArrayList<>(current));
+            return;
+        }
+        for (Map.Entry<Integer, Integer> entry : frequencies.entrySet()) {
+            if (entry.getValue() > 0) {
+                entry.setValue(entry.getValue() - 1);
+                current.add(entry.getKey());
+                permuteUnique(array, result, frequencies, current);
+                current.removeLast();
+                entry.setValue(entry.getValue() + 1);
+            }
+        }
+    }
+
+    private Map<Integer, Integer> getFrequencies(int[] array) {
+        final Map<Integer, Integer> frequencies = new HashMap<>();
+        for (int element : array) {
+            frequencies.put(element, frequencies.getOrDefault(element, 0) + 1);
+        }
+        return frequencies;
+    }
+}