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30 lines
702 B
Python
30 lines
702 B
Python
#!/usr/bin/env python3
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"""
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Given an array of integers and an integer req_sum, find the number of pairs of array
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elements whose sum is equal to req_sum.
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https://practice.geeksforgeeks.org/problems/count-pairs-with-given-sum5022/0
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"""
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from itertools import combinations
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def pairs_with_sum(arr: list, req_sum: int) -> int:
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"""
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Return the no. of pairs with sum "sum"
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>>> pairs_with_sum([1, 5, 7, 1], 6)
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2
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>>> pairs_with_sum([1, 1, 1, 1, 1, 1, 1, 1], 2)
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28
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>>> pairs_with_sum([1, 7, 6, 2, 5, 4, 3, 1, 9, 8], 7)
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4
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"""
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return len([1 for a, b in combinations(arr, 2) if a + b == req_sum])
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if __name__ == "__main__":
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from doctest import testmod
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testmod()
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