From 3c6068e7ffbcd39a29cd41755c9696bd3f4be288 Mon Sep 17 00:00:00 2001
From: Tidimatso Anthony <167877348+tidianthony@users.noreply.github.com>
Date: Tue, 3 Sep 2024 19:02:29 +0200
Subject: [PATCH 1/2] Update pairs_with_given_sum.py
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Dictionary Usage:

We use a dictionary seen to keep track of the number of times each number has appeared so far.
For each number num in the array, we calculate its complement (req_sum - num). If this complement has been seen before, then it means there are pairs that sum up to req_sum, and we add the count of such complements to our count.
Efficiency:

This approach processes each element of the array exactly once and performs operations in constant time for each element. Thus, the time complexity is
𝑂
(
𝑛
)
O(n), where
𝑛
n is the number of elements in the array.
Readability:

The code is more straightforward and easier to understand compared to generating combinations. It leverages hash maps for efficient lookups and counting.
---
 .../arrays/pairs_with_given_sum.py            | 26 +++++++++++++------
 1 file changed, 18 insertions(+), 8 deletions(-)

diff --git a/data_structures/arrays/pairs_with_given_sum.py b/data_structures/arrays/pairs_with_given_sum.py
index b27bd78e1e0f..9faf483bd331 100644
--- a/data_structures/arrays/pairs_with_given_sum.py
+++ b/data_structures/arrays/pairs_with_given_sum.py
@@ -7,12 +7,10 @@
 https://practice.geeksforgeeks.org/problems/count-pairs-with-given-sum5022/0
 """
 
-from itertools import combinations
-
-
-def pairs_with_sum(arr: list, req_sum: int) -> int:
+def pairs_with_sum(arr: list[int], req_sum: int) -> int:
     """
-    Return the no. of pairs with sum "sum"
+    Return the number of pairs with sum equal to req_sum.
+    
     >>> pairs_with_sum([1, 5, 7, 1], 6)
     2
     >>> pairs_with_sum([1, 1, 1, 1, 1, 1, 1, 1], 2)
@@ -20,10 +18,22 @@ def pairs_with_sum(arr: list, req_sum: int) -> int:
     >>> pairs_with_sum([1, 7, 6, 2, 5, 4, 3, 1, 9, 8], 7)
     4
     """
-    return len([1 for a, b in combinations(arr, 2) if a + b == req_sum])
-
+    count = 0
+    seen = {}
+    
+    for num in arr:
+        complement = req_sum - num
+        if complement in seen:
+            count += seen[complement]
+        
+        if num in seen:
+            seen[num] += 1
+        else:
+            seen[num] = 1
+    
+    return count
 
 if __name__ == "__main__":
     from doctest import testmod
-
     testmod()
+

From 881b4eddd25f63958ff6bf1025085b320541cd06 Mon Sep 17 00:00:00 2001
From: "pre-commit-ci[bot]"
 <66853113+pre-commit-ci[bot]@users.noreply.github.com>
Date: Tue, 3 Sep 2024 17:04:45 +0000
Subject: [PATCH 2/2] [pre-commit.ci] auto fixes from pre-commit.com hooks

for more information, see https://pre-commit.ci
---
 data_structures/arrays/pairs_with_given_sum.py | 12 +++++++-----
 1 file changed, 7 insertions(+), 5 deletions(-)

diff --git a/data_structures/arrays/pairs_with_given_sum.py b/data_structures/arrays/pairs_with_given_sum.py
index 9faf483bd331..53c2b031f729 100644
--- a/data_structures/arrays/pairs_with_given_sum.py
+++ b/data_structures/arrays/pairs_with_given_sum.py
@@ -7,10 +7,11 @@
 https://practice.geeksforgeeks.org/problems/count-pairs-with-given-sum5022/0
 """
 
+
 def pairs_with_sum(arr: list[int], req_sum: int) -> int:
     """
     Return the number of pairs with sum equal to req_sum.
-    
+
     >>> pairs_with_sum([1, 5, 7, 1], 6)
     2
     >>> pairs_with_sum([1, 1, 1, 1, 1, 1, 1, 1], 2)
@@ -20,20 +21,21 @@ def pairs_with_sum(arr: list[int], req_sum: int) -> int:
     """
     count = 0
     seen = {}
-    
+
     for num in arr:
         complement = req_sum - num
         if complement in seen:
             count += seen[complement]
-        
+
         if num in seen:
             seen[num] += 1
         else:
             seen[num] = 1
-    
+
     return count
 
+
 if __name__ == "__main__":
     from doctest import testmod
-    testmod()
 
+    testmod()