3Sum solution

Author: jungsiroo

3sum/jungsiroo.py

@@ -0,0 +1,41 @@
+class Solution:
+    def threeSum(self, nums: List[int]) -> List[List[int]]:
+        # Naive Solution
+        # Tc : O(n^3) / Sc : O(nC_3)
+        
+        n = len(nums)
+        """
+        for i in range(n-2):
+            for j in range(i+1,n-1):
+                for k in range(j+1, n):
+                    if nums[i]+nums[j]+nums[k] == 0:
+                        ret.add(tuple(sorted([nums[i], nums[j], nums[k]])))
+
+        ret = [x for x in ret]
+        return ret 
+        """
+
+        # Better Solution
+        # two-sum question with fixed num (traversal in for loop)
+        # Tc : O(n^2) / Sc : O(n)
+        ret = []
+        nums.sort()
+
+        for i in range(n):
+            if i>0 and nums[i] == nums[i-1]:
+                continue
+            j, k = i+1, n-1
+
+            while j < k:
+                sum_ = nums[i] + nums[j] + nums[k]
+                if sum_ < 0 : j += 1
+                elif sum_ > 0 : k -= 1
+                else:
+                    ret.append([nums[i], nums[j], nums[k]])
+                    j += 1
+                
+                    while nums[j] == nums[j-1] and j<k:
+                        j += 1
+            
+        return ret
+