Count Song Pairs Whose Combined Duration Is a Multiple of Sixty
Company: Amazon
Role: Software Engineer
Category: Coding & Algorithms
Difficulty: medium
Interview Round: Other
### Problem
For song durations in `time`, count index pairs i<j whose sum is divisible by60. Repeated durations still represent different songs at different indices.
```cpp
class Solution {
public:
int numPairsDivisibleBy60(vector<int>& time);
};
```
### Examples
**Example 1:**
```text
Input: time = [10,50,70,110]
Output: 4
Explanation: Each of the two duration-remainder10 songs pairs with either of the two remainder50 songs.
```
**Example 2:**
```text
Input: time = [30,30,90,5]
Output: 3
Explanation: Any two of the three remainder30 songs form a multiple-of60 sum. The duration5 song has no partner.
```
### Constraints
- `1 <= time.length <= 6*10^4`.
- `1 <= time[i] <= 500`.
### Contract considerations
Only distinct indices may pair, and input order is irrelevant to which pairs qualify.
```hint Read the boundary condition
Only each duration modulo60 matters when finding earlier partners.
```
### Boundary reminders
Only distinct indices may pair, and input order is irrelevant to which pairs qualify.
Overview: Count Song Pairs Whose Combined Duration Is a Multiple of Sixty. For song durations in time, count index pairs i<j whose sum is divisible by60.
