Refactor has_pair_with_sum to use a set for O(n) lookup

Author: Fatma Degirmenci

Sprint-1/Python/has_pair_with_sum/has_pair_with_sum.py

@@ -7,12 +7,13 @@ def has_pair_with_sum(numbers: List[Number], target_sum: Number) -> bool:
     """
     Find if there is a pair of numbers that sum to a target value.
 
-    Time Complexity:
-    Space Complexity:
-    Optimal time complexity:
+    Time Complexity: We have nested loop --> O(n*n)
+    Space Complexity:We have variables -->O(1)
+    Optimal time complexity:We can use only one loop -->O(n)
     """
-    for i in range(len(numbers)):
-        for j in range(i + 1, len(numbers)):
-            if numbers[i] + numbers[j] == target_sum:
-                return True
+    seen = set()
+    for num in numbers:
+        if target_sum - num in seen:
+            return True
+        seen.add(num)
     return False