update 0046.全排列: 替换 go 代码

problems/0046.全排列.md

@@ -275,29 +275,34 @@ class Solution:
 
 ### Go 
 ```Go
-var res [][]int
+var (
+    res [][]int
+    path  []int
+    st    []bool   // state的缩写
+)
 func permute(nums []int) [][]int {
-	res = [][]int{}
-	backTrack(nums,len(nums),[]int{})
-	return res
-}
-func backTrack(nums []int,numsLen int,path []int)  {
-	if len(nums)==0{
-		p:=make([]int,len(path))
-		copy(p,path)
-		res = append(res,p)
-	}
-	for i:=0;i<numsLen;i++{
-		cur:=nums[i]
-		path = append(path,cur)
-		nums = append(nums[:i],nums[i+1:]...)//直接使用切片
-		backTrack(nums,len(nums),path)
-		nums = append(nums[:i],append([]int{cur},nums[i:]...)...)//回溯的时候切片也要复原，元素位置不能变
-		path = path[:len(path)-1]
-
-	}
+    res, path = make([][]int, 0), make([]int, 0, len(nums))
+    st = make([]bool, len(nums))
+    dfs(nums, 0)
+    return res
 }
 
+func dfs(nums []int, cur int) {
+    if cur == len(nums) {
+        tmp := make([]int, len(path))
+        copy(tmp, path)
+        res = append(res, tmp)
+    }
+    for i := 0; i < len(nums); i++ {
+        if !st[i] {
+            path = append(path, nums[i])
+            st[i] = true
+            dfs(nums, cur + 1)
+            st[i] = false
+            path = path[:len(path)-1]
+        }
+    }
+}
 ```
 
 ### Javascript