permutations II

Author: fishercoder1534

MEDIUM/src/medium/PermutationsII.java

@@ -0,0 +1,51 @@
+package medium;
+
+import java.util.ArrayList;
+import java.util.Arrays;
+import java.util.List;
+
+import utils.CommonUtils;
+
+public class PermutationsII {
+    /**Looked at this post: https://discuss.leetcode.com/topic/31445/really-easy-java-solution-much-easier-than-the-solutions-with-very-high-vote*/
+    public List<List<Integer>> permuteUnique(int[] nums) {
+        List<List<Integer>> result = new ArrayList();
+        if (nums == null || nums.length == 0) return result;
+        boolean[] used = new boolean[nums.length];
+        List<Integer> list = new ArrayList();
+        Arrays.sort(nums);
+        dfs(nums, used, list, result);
+        return result;
+    }
+
+    
+    private void dfs(int[] nums, boolean[] used, List<Integer> list, List<List<Integer>> result) {
+        if (list.size() == nums.length){
+            result.add(new ArrayList(list));
+            return;
+        }
+        for (int i = 0; i < nums.length; i++){
+            if (used[i]) continue;
+            if (i > 0 && nums[i - 1] == nums[i] && !used[i - 1])
+                continue;
+            /**
+             * For this line, both !used[i-1] and used[i-1] will AC. It is because the first one makes sure when
+             * duplicates are selected, the order is ascending (index from small to large). However,
+             * the second one means the descending order.
+             */
+            used[i] = true;
+            list.add(nums[i]);
+            dfs(nums, used, list, result);
+            used[i] = false;
+            list.remove(list.size()-1);
+        }
+    }
+
+
+    public static void main(String...args){
+        int[] nums = new int[]{1,1,2};
+        PermutationsII test = new PermutationsII();
+        List<List<Integer>> result = test.permuteUnique(nums);
+        CommonUtils.printIntegerList(result);
+    }
+}

README.md

@@ -115,6 +115,7 @@
 |67|[Add Binary](https://leetcode.com/problems/add-binary/)|[Solution](../../blob/master/EASY/src/easy/AddBinary.java)|O(n)|O(1)|Easy|
 |58|[Length of Last Word](https://leetcode.com/problems/length-of-last-word/)|[Solution](../../blob/master/EASY/src/easy/LengthofLastWord.java)|O(n)|O(1)|Easy|
 |56|[Merge Intervals](https://leetcode.com/problems/merge-intervals/)|[Solution](../../blob/master/HARD/src/hard/MergeIntervals.java)|O(n*logn)|O(1)|Hard|
+|47|[Permutations II](https://leetcode.com/problems/permutations-ii/)|[Solution](../../blob/master/MEDIUM/src/medium/PermutationsII.java)|O(n*n!)|O(n)|Medium|Backtracking
 |43|[Multiply Strings](https://leetcode.com/problems/multiply-strings/)|[Solution]|||Medium
 |31|[Next Permutation](https://leetcode.com/problems/next-permutation)|[Solution](../../blob/master/MEDIUM/src/medium/NextPermutation.java)|O(n)|O(1)|Medium|Array
 |24|[Swap Nodes in Pairs](https://leetcode.com/problems/swap-nodes-in-pairs/)|[Solution](../../blob/master/EASY/src/easy/SwapNodesinPairs.java)|O(n)|O(1)|Easy| Recursion, LinkedList