Merge pull request youngyangyang04#876 from Younglesszzz/master

更新回溯的另一种写法 全排列Ⅱ Java版本

Author: youngyangyang04

problems/回溯算法去重问题的另一种写法.md

@@ -249,6 +249,45 @@ used数组可是全局变量，每层与每层之间公用一个used数组，所
 
 
 Java：
+**47.全排列II**
+
+
+```java
+class Solution {
+    private List<List<Integer>> res = new ArrayList<>();
+    private List<Integer> path = new ArrayList<>();
+    private boolean[] used = null;
+
+    public List<List<Integer>> permuteUnique(int[] nums) {
+        used = new boolean[nums.length];
+        Arrays.sort(nums);
+        backtracking(nums);
+        return res;
+    }
+
+    public void backtracking(int[] nums) {
+        if (path.size() == nums.length) {
+            res.add(new ArrayList<>(path));
+            return;
+        }
+        HashSet<Integer> hashSet = new HashSet<>();//层去重
+        for (int i = 0; i < nums.length; i++) {
+            if (hashSet.contains(nums[i]))
+                continue;
+            if (used[i] == true)//枝去重
+                continue;
+            hashSet.add(nums[i]);//记录元素
+            used[i] = true;
+            path.add(nums[i]);
+            backtracking(nums);
+            path.remove(path.size() - 1);
+            used[i] = false;
+        }
+    }
+}
+
+```
+
 
 Python：