1010. Pairs of Songs With Total Durations Divisible by 60

Problem

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 * 10^4

• 1 <= time[i] <= 500

Solution (Java)

class Solution {
    public int numPairsDivisibleBy60(int[] time) {
        int[] remainder = new int[60];
        int ans = 0;
        for (int j : time) {
            int rem = j % 60;
            if (rem == 0) {
                ans += remainder[0];
            } else {
                ans += remainder[60 - rem];
            }
            remainder[rem]++;
        }
        return ans;
    }
}

Explain:

nope.

Complexity:

• Time complexity : O(n).
• Space complexity : O(n).