scammingthecodinginterview.com : Problem 012 : Bishops attacking each other

bishops_attacking_each_other.py

"""
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"""
from fractions import Fraction
from functools import reduce
from operator import mul


def find_bishop_pairs_attacking_each_other(n, m, bishops):

    coordinate_sum_map = {}
    coordinate_diff_map = {}

    for b in bishops:
        sum = b[0] + b[1]
        diff = b[0] - b[1]

        coordinate_diff_map[diff] = coordinate_diff_map.get(diff, 0) + 1
        coordinate_sum_map[sum] = coordinate_sum_map.get(sum, 0) + 1

    attacking_pairs = 0

    for k, v in coordinate_sum_map.items():
        temp = nCk(v, 2)
        attacking_pairs += temp

    for k, v in coordinate_diff_map.items():
        temp = nCk(v, 2)
        attacking_pairs += temp

    return attacking_pairs


def nCk(n,k):
    return int(reduce(mul, (Fraction(n-i, i+1) for i in range(k)), 1))


if __name__ == '__main__':

    m = 5

    n = int(input())

    bishops = []

    for i in range(0, n):
        temp = input().split(" ")
        x = int(temp[0])
        y = int(temp[1])
        bishops.append((x, y))

    # bishops = [(1, 1), (1, 5), (3, 3), (5, 1), (5, 5)]

    attacks = find_bishop_pairs_attacking_each_other(0, 0, bishops)

    print(attacks)