Pairs of Songs With Total Durations Divisible by 60 (M)

題目

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

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

題意

在陣列中找一對數，使它們的和能被60整除，求這樣的數對的個數。

思路

Hash。遍歷陣列，計算當前數除以60的餘數R，如果R為0，在結果上加上之前餘數為0的數的個數；如果R不為0，在結果上加上之前餘數為60-R的數的個數。

程式碼實現

Java

class Solution {
    public int numPairsDivisibleBy60(int[] time) {
        int count = 0;
        int[] remainders = new int[60];

        for (int num : time) {
            int remainder = num % 60;
            if (remainder == 0) {
                count += remainders[0];
            } else {
                count += remainders[60 - remainder];
            }
            remainders[remainder]++;
        }

        return count;
    }
}