Create 4Sum.py

Author: sudoshivesh

medium/4Sum.py

@@ -0,0 +1,31 @@
+#18. 4Sum
+class Solution:
+  def fourSum(self, nums: List[int], target: int):
+    ans = []
+
+    def nSum(l: int, r: int, target: int, n: int, path: List[int], ans: List[List[int]]) -> None:
+      if r - l + 1 < n or n < 2 or target < nums[l] * n or target > nums[r] * n:
+        return
+      if n == 2:
+        while l < r:
+          summ = nums[l] + nums[r]
+          if summ == target:
+            ans.append(path + [nums[l], nums[r]])
+            l += 1
+            while nums[l] == nums[l - 1] and l < r:
+              l += 1
+          elif summ < target:
+            l += 1
+          else:
+            r -= 1
+        return
+
+      for i in range(l, r + 1):
+        if i > l and nums[i] == nums[i - 1]:
+          continue
+
+        nSum(i + 1, r, target - nums[i], n - 1, path + [nums[i]], ans)
+
+    nums.sort()
+    nSum(0, len(nums) - 1, target, 4, [], ans)
+    return ans