Python Maximum Pairwise Product time limit exceeded error

Question

n = int(input())
a = [int(x) for x in input().split()]
product = 0
for i in range(n):
  for j in range(i + 1, n):
    product = max(product, a[i] * a[j])
print(product)

When I submit the above code to Corsera's coding judge system,

Failed case #4/17: time limit exceeded (Time used: 9.98/5.00, memory used: 20918272/536870912.)

has been returned. How can I change it?

Answer 1

It is in O(n^2). You can sort a and choose two larger value in a as a result in O(n log(n)) (if the input value for list a is positive).

input_list = sorted(a)
product = max(a[0]*a[1], a[-1] * a[-2]) #as suggested in comments if there is negative values

Answer 2

首先以降序对项目进行排序，然后将已排序列表中的第一和第二项相乘（当然，如果所有结果都是肯定的），会不会花费更少的时间？