Created
October 9, 2019 02:15
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Maximum Pairwise Product Algorithm
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| # maximum pairwise product | |
| # find the maximum product of two distinct numbers in a sequence of | |
| # non-negative integers | |
| # input: sequence of non-negative integers | |
| # output: maximum value that can be obtained by multiplying two different | |
| # elements from the sequence | |
| import random | |
| def maximum_pairwise_product(a): | |
| product = 0 | |
| n = len(a) | |
| for i in range(n): | |
| for j in range(i + 1, n): | |
| product = max(product, a[i] * a[j]) | |
| return product | |
| def maximum_pairwise_product_fast(a): | |
| n = len(a) | |
| max_index1 = 0 | |
| for i in range(n): | |
| if a[i] > a[max_index1]: | |
| max_index1 = i | |
| if max_index1 == 0: | |
| max_index2 = 1 | |
| else: | |
| max_index2 = 0 | |
| for i in range(n): | |
| if i != max_index1 and a[i] > a[max_index2]: | |
| max_index2 = i | |
| return a[max_index1] * a[max_index2] | |
| def generate_array(): | |
| n = random.randint(2, 10000) | |
| a = [] | |
| while n > 0: | |
| a.append(random.randint(0, 100000)) | |
| n -= 1 | |
| return a | |
| def stress_test(a): | |
| while True: | |
| a = generate_array() | |
| # print(a) | |
| slow = maximum_pairwise_product(a) | |
| fast = maximum_pairwise_product_fast(a) | |
| if slow == fast: | |
| print("OK") | |
| else: | |
| print("slow {0} does not equal fast {1}", slow, fast) | |
| break | |
| a = generate_array() | |
| stress_test(a) |
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