Merge pull request #2644 from markwang1992/90-subsetsWithDup

90.子集II增加Go使用used数组解法

Author: youngyangyang04

problems/0090.子集II.md

@@ -310,6 +310,43 @@ class Solution:
 ```
 ### Go 
 
+使用used数组
+```Go
+var (
+    result [][]int
+    path []int
+)
+
+func subsetsWithDup(nums []int) [][]int {
+    result = make([][]int, 0)
+    path = make([]int, 0)
+    used := make([]bool, len(nums))
+    sort.Ints(nums) // 去重需要排序
+    backtracing(nums, 0, used)
+    return result
+}
+
+func backtracing(nums []int, startIndex int, used []bool) {
+    tmp := make([]int, len(path))
+    copy(tmp, path)
+    result = append(result, tmp)
+    for i := startIndex; i < len(nums); i++ {
+        // used[i - 1] == true，说明同一树枝candidates[i - 1]使用过
+        // used[i - 1] == false，说明同一树层candidates[i - 1]使用过
+        // 而我们要对同一树层使用过的元素进行跳过
+        if i > 0 && nums[i] == nums[i-1] && used[i-1] == false {
+            continue
+        }
+        path = append(path, nums[i])
+        used[i] = true
+        backtracing(nums, i + 1, used)
+        path = path[:len(path)-1]
+        used[i] = false
+    }
+}
+```
+
+不使用used数组
 ```Go
 var (
     path   []int