Pairs of Songs With Total Durations Divisible by 60 in Python

Suppose we have a list of songs, the i-th song has a duration of time[i] seconds. We have to find the number of pairs of songs for which their total time in seconds is divisible by 60.

So if the time array is like [30, 20, 150, 100, 40], then the answer will be 3. Three pairs will be (3, 150), (20, 100), (20, 40) for all cases the total duration is divisible by 60.

To solve this, we will follow these steps −

• Take a map rem to store remainders. Set ans := 0
• for all elements i in time −
  • if i is divisible by 0 and 0 in rem, then ans := ans + rem[0]
  • o otherwise when 60 – (i mod 60) in rem, then ans := ans + rem[60 – (i mod 60)]
  • if i mod 60 in rem, then rem[i mod 60] := rem[i mod 60] + 1
  • otherwise rem[i mod 60] := 1
• return the ans

Example

Let us see the following implementation to get better understanding −

 Live Demo

class Solution(object):
   def numPairsDivisibleBy60(self, time):
      ans = 0
      remainder = {}
      for i in time:
         if i % 60 == 0 and 0 in remainder:
            ans += remainder[0]
         elif 60 - (i%60) in remainder:
            ans += remainder[60 - (i%60)]
         if i % 60 in remainder:
            remainder[i%60]+=1
         else:
            remainder[i%60]=1
      return ans
ob1 = Solution()
print(ob1.numPairsDivisibleBy60([30,20,150,100,40]))

Input

[30,20,150,100,40]

Output

3