Update 0046.全排列.md

更新Java版本

problems/0046.全排列.md

@@ -147,7 +147,41 @@ public:
 
 
 Java：
+```java
+class Solution {
+    List<List<Integer>> result = new ArrayList<>();// 存放符合条件结果的集合
+    LinkedList<Integer> path = new LinkedList<>();// 用来存放符合条件结果
+    boolean[] used;
+    public List<List<Integer>> permute(int[] nums) {
+        if (nums.length == 0){
+            return result;
+        }
+        used = new boolean[nums.length];
+        permuteHelper(nums);
+        return result;
+    }
 
+    private void permuteHelper(int[] nums){
+        if (path.size() == nums.length){
+            result.add(new ArrayList<>(path));
+            return;
+        }
+        for (int i = 0; i < nums.length; i++){
+            // if (path.contains(nums[i])){
+            //     continue;
+            // }
+            if (used[i]){
+                continue;
+            }
+            used[i] = true;
+            path.add(nums[i]);
+            permuteHelper(nums);
+            path.removeLast();
+            used[i] = false;
+        }
+    }
+}
+```
 
 Python：