1010. Pairs of Songs With Total Durations Divisible by 60

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1010. Pairs of Songs With Total Durations Divisible by 60

Description

You are given a list of songs where the i^th 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:

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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:

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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

Hints/Notes

Solution

Language: C++

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class Solution {
public:
    int numPairsDivisibleBy60(vector<int>& time) {
        unordered_map<int, int> m;
        int res = 0;
        for (int& t : time) {
            int target = (60 - t % 60) % 60;
            res += m[target];
            m[t % 60]++;
        }
        return res;
    }
};