diff --git a/problems/0018.四数之和.md b/problems/0018.四数之和.md
index 8606b2eb..4fee8358 100644
--- a/problems/0018.四数之和.md
+++ b/problems/0018.四数之和.md
@@ -209,34 +209,38 @@ class Solution {
 Python：
 (版本一) 双指针
 ```python
- def fourSum(self, nums: List[int], target: int) -> List[List[int]]:
-        result = []
+class Solution:
+    def fourSum(self, nums: List[int], target: int) -> List[List[int]]:
         nums.sort()
-        for k in range(len(nums)):
-            if nums[k] > target and nums[k] >= 0:
+        n = len(nums)
+        result = []
+        for i in range(n):
+            if nums[i] > target and nums[i] > 0 and target > 0:# 剪枝（可省）
                 break
-            if k > 0 and nums[k] == nums[k-1]:
+            if i > 0 and nums[i] == nums[i-1]:# 去重
                 continue
-            for i in range(k+1, len(nums)):
-                if nums[k] + nums[i] > target and nums[k] + nums[i] >= 0:
+            for j in range(i+1, n):
+                if nums[i] + nums[j] > target and target > 0: #剪枝（可省）
                     break
-                if i > k+1 and nums[i] == nums[i-1]:
+                if j > i+1 and nums[j] == nums[j-1]: # 去重
                     continue
-                left, right = i+1, len(nums)-1
-                while right > left:
-                    if nums[k] + nums[i] + nums[left] + nums[right] > target:
+                left, right = j+1, n-1
+                while left < right:
+                    s = nums[i] + nums[j] + nums[left] + nums[right]
+                    if s == target:
+                        result.append([nums[i], nums[j], nums[left], nums[right]])
+                        while left < right and nums[left] == nums[left+1]:
+                            left += 1
+                        while left < right and nums[right] == nums[right-1]:
+                            right -= 1
+                        left += 1
                         right -= 1
-                    elif nums[k] + nums[i] + nums[left] + nums[right] < target:
+                    elif s < target:
                         left += 1
                     else:
-                        result.append([nums[k], nums[i], nums[left], nums[right]])
-                        while right > left and nums[right] == nums[right-1]:
-                            right -= 1
-                        while right > left and nums[left] == nums[left+1]:
-                            left += 1
                         right -= 1
-                        left += 1
         return result
+
 ```
 (版本二) 使用字典