Add solution 047

Author: yanglbme

README.md

@@ -34,6 +34,7 @@ Complete solutions to Leetcode problems, updated daily.
 | 019 | [Remove Nth Node From End of List](https://github.com/yanglbme/leetcode/tree/master/solution/019.Remove%20Nth%20Node%20From%20End%20of%20List) | `Linked List`, `Two Pointers` |
 | 024 | [Swap Nodes in Pairs](https://github.com/yanglbme/leetcode/tree/master/solution/024.Swap%20Nodes%20in%20Pairs) | `Linked List` |
 | 046 | [Permutations](https://github.com/yanglbme/leetcode/tree/master/solution/046.Permutations) | `Backtracking` |
+| 047 | [Permutations II](https://github.com/yanglbme/leetcode/tree/master/solution/047.Permutations%20II) | `Backtracking` |
 | 062 | [Unique Paths](https://github.com/yanglbme/leetcode/tree/master/solution/062.Unique%20Paths) | `Array`, `Dynamic Programming` |
 | 063 | [Unique Paths II](https://github.com/yanglbme/leetcode/tree/master/solution/063.Unique%20Paths%20II) | `Array`, `Dynamic Programming` |
 | 082 | [Remove Duplicates from Sorted List II](https://github.com/yanglbme/leetcode/tree/master/solution/082.Remove%20Duplicates%20from%20Sorted%20List%20II) | `Linked List` |

solution/047.Permutations II/README.md

@@ -0,0 +1,65 @@
+## 全排列 II
+### 题目描述
+
+给定一个可包含重复数字的序列，返回所有不重复的全排列。
+
+示例:
+```
+输入: [1,1,2]
+输出:
+[
+  [1,1,2],
+  [1,2,1],
+  [2,1,1]
+]
+```
+
+### 解法
+将数组的首元素依次与数组的每个元素交换(两元素不相等才进行交换)，对于每一轮交换，对后面的数组进行递归调用。当元素只剩下一个时，添加此时的数组到 list 中。
+
+```java
+class Solution {
+    public List<List<Integer>> permuteUnique(int[] nums) {
+        List<List<Integer>> list = new ArrayList<>();
+        permute(list, nums, 0);
+        return list;
+    }
+    
+    private void permute(List<List<Integer>> list, int[] nums, int start) {
+        int end = nums.length - 1;
+        if (start == end) {
+            List<Integer> tmp = new ArrayList<>();
+            for (int val : nums) {
+                tmp.add(val);
+            }
+            
+            // 已存在，则不添加
+            if (!list.contains(tmp)) {
+                list.add(tmp);
+                return;
+            }
+            
+        }
+        
+        for (int i = start; i <= end; ++i) {
+            if (i == start) {
+                permute(list, nums, start + 1);
+            } else if (nums[i] != nums[start]) {
+                // i 与 start 不相等，且对应的数组值也不相等，才进行交换
+                swap(nums, i, start);
+                permute(list, nums, start + 1);
+                swap(nums, i, start);
+            }
+            
+        }
+        
+        
+    }
+    
+    private static void swap(int[] nums, int i, int j) {
+        int t = nums[i];
+        nums[i] = nums[j];
+        nums[j] = t;
+    }
+}
+```

solution/047.Permutations II/Solution.java

@@ -0,0 +1,43 @@
+class Solution {
+    public List<List<Integer>> permuteUnique(int[] nums) {
+        List<List<Integer>> list = new ArrayList<>();
+        permute(list, nums, 0);
+        return list;
+    }
+
+    private void permute(List<List<Integer>> list, int[] nums, int start) {
+        int end = nums.length - 1;
+        if (start == end) {
+            List<Integer> tmp = new ArrayList<>();
+            for (int val : nums) {
+                tmp.add(val);
+            }
+
+            // 已存在，则不添加
+            if (!list.contains(tmp)) {
+                list.add(tmp);
+                return;
+            }
+
+        }
+
+        for (int i = start; i <= end; ++i) {
+            if (i == start) {
+                permute(list, nums, start + 1);
+            } else if (nums[i] != nums[start]) {
+                // i 与 start 不相等，且对应的数组值也不相等，才进行交换
+                swap(nums, i, start);
+                permute(list, nums, start + 1);
+                swap(nums, i, start);
+            }
+
+        }
+
+    }
+
+    private static void swap(int[] nums, int i, int j) {
+        int t = nums[i];
+        nums[i] = nums[j];
+        nums[j] = t;
+    }
+}