#1010 - Pairs of Songs With Total Durations Divisible by 60

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Problem Description

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.

Solution

/**
 * @param {number[]} time
 * @return {number}
 */
var numPairsDivisibleBy60 = function(time) {
  const mods = new Array(60).fill(0);
  return time.reduce((sum, t) => {
    sum += mods[(60 - t % 60) % 60];
    mods[t % 60]++;
    return sum;
  }, 0);
};