1010. Pairs of Songs With Total Durations Divisible by 60

Problem Link

Description

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You are given a list of songs where the ith song has a duration of time[i] seconds.

Return the number of pairs of songs for which their total duration in seconds is divisible by 60. Formally, we want the number of indices i, j such that i < j with (time[i] + time[j]) % 60 == 0.

 

Example 1:

Input: time = [30,20,150,100,40]
Output: 3
Explanation: Three pairs have a total duration divisible by 60:
(time[0] = 30, time[2] = 150): total duration 180
(time[1] = 20, time[3] = 100): total duration 120
(time[1] = 20, time[4] = 40): total duration 60

Example 2:

Input: time = [60,60,60]
Output: 3
Explanation: All three pairs have a total duration of 120, which is divisible by 60.

 

Constraints:

• 1 <= time.length <= 6 * 104
• 1 <= time[i] <= 500

Solution

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Python3

class Solution:
    def numPairsDivisibleBy60(self, time: List[int]) -> int:
        mp = defaultdict(int)
        res = 0
 
        for x in time:
            x %= 60
 
            if x == 0:
                res += mp[x]
            else:
                res += mp[60 - x]
            mp[x] += 1
        
        return res