modified 15. Add a new version with the same idea.

problems/0015.三数之和.md

@@ -243,7 +243,34 @@ class Solution:
                     right -= 1
         return ans
 ```
+Python (v2):
+
+```python
+class Solution:
+    def threeSum(self, nums: List[int]) -> List[List[int]]:
+        if len(nums) < 3: return []
+        nums, res = sorted(nums), []
+        for i in range(len(nums) - 2):
+            cur, l, r = nums[i], i + 1, len(nums) - 1
+            if res != [] and res[-1][0] == cur: continue # Drop duplicates for the first time.
+
+            while l < r:
+                if cur + nums[l] + nums[r] == 0:
+                    res.append([cur, nums[l], nums[r]])
+                    # Drop duplicates for the second time in interation of l & r. Only used when target situation occurs, because that is the reason for dropping duplicates.
+                    while l < r - 1 and nums[l] == nums[l + 1]:
+                        l += 1
+                    while r > l + 1 and nums[r] == nums[r - 1]:
+                        r -= 1
+                if cur + nums[l] + nums[r] > 0:
+                    r -= 1
+                else:
+                    l += 1
+        return res
+```
+
 Go：
+
 ```Go
 func threeSum(nums []int)[][]int{
 	sort.Ints(nums)