Syntax error Program to find number of quadruples for which product of first and last pairs are same in Python

Program to find number of quadruples for which product of first and last pairs are same in Python

Suppose we have a list of numbers called nums, with unique positive numbers nums. We have to find the number of quadruples like (a, b, c, d) from nums such that a*b = c*d, a, b, c and d all are distinct elements of nums.

So, if the input is like nums = [3, 6, 4, 8], then the output will be 8, because the quadruples are [[3,8,6,4], [3,8,4,6], [8,3,6,4], [8,3,4,6], [6,4,3,8], [4,6,3,8], [6,4,8,3], [4,6,8,3]].

To solve this, we will follow these steps −

  • c := a new map
  • n := size of nums
  • for i in range 0 to n - 1, do
    • for j in range i + 1 to n - 1, do
      • x := nums[i] * nums[j]
      • c[x] := 1 + (c[x] if available, otherwise 0)
  • ret := 0
  • for each x in list of all values in c, do
    • ret := ret + x *(x - 1)
  • return ret * 4

Example

Let us see the following implementation to get better understanding −

def solve(nums):
   c = {}
   n = len(nums)
   for i in range(n):
      for j in range(i + 1, n):
         x = nums[i] * nums[j]
         c[x] = c.get(x, 0) + 1
   ret = 0
   for x in c.values():
      ret += x * (x - 1)
   return ret * 4

nums = [3, 6, 4, 8]
print(solve(nums))

Input

[3, 6, 4, 8]

Output

8
Updated on: 2021-10-18T12:51:58+05:30

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