Update pairs_with_given_sum.py

[ghost]

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.

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• Add an algorithm?
• Fix a bug or typo in an existing algorithm?
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