diff --git a/problems/0213.打家劫舍II.md b/problems/0213.打家劫舍II.md
index cd9d596d..385c5867 100644
--- a/problems/0213.打家劫舍II.md
+++ b/problems/0213.打家劫舍II.md
@@ -225,32 +225,38 @@ class Solution:
 // 打家劫舍Ⅱ 动态规划
 // 时间复杂度O(n) 空间复杂度O(n)
 func rob(nums []int) int {
-    if len(nums) == 1 {
-        return nums[0]
+    // 如果长度为0或1，那么有没有环的限制都一样
+    if len(nums) <= 1 {
+        return robWithoutCircle(nums)
     }
-    if len(nums) == 2 {
-        return max(nums[0], nums[1])
-    }
-    
-    result1 := robRange(nums, 0)
-    result2 := robRange(nums, 1)
-    return max(result1, result2)
+
+    // 否则，去头或去尾，取最大
+    res1 := robWithoutCircle(nums[:len(nums)-1])
+    res2 := robWithoutCircle(nums[1:])
+
+    return max(res1, res2)
 }
 
-// 偷盗指定的范围
-func robRange(nums []int, start int) int {
+// 原始的打家劫舍版
+func robWithoutCircle(nums []int) int {
+    switch len(nums) {
+        case 0: return 0
+        case 1: return nums[0]
+    }
     dp := make([]int, len(nums))
-    dp[1] = nums[start]
-    
-    for i := 2; i < len(nums); i++ {
-        dp[i] = max(dp[i - 2] + nums[i - 1 + start], dp[i - 1])
+    dp[0]=nums[0]
+    dp[1] = max(nums[0], nums[1])
+
+    for i:=2; i<len(nums); i++ {
+        dp[i] = max(dp[i-1], dp[i-2]+nums[i])
     }
-    
-    return dp[len(nums) - 1]
+
+    return dp[len(nums)-1]
+
 }
 
-func max(a, b int) int {
-    if a > b {
+func max(a, b int ) int {
+    if a>b {
         return a
     }
     return b