Pairs of Songs With Total Durations Divisible by 60 - Array - Easy - LeetCode

In a list of songs, 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:

Input: [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: [60,60,60]

Output: 3

Explanation: All three pairs have a total duration of 120, which is divisible by 60.

Note:

1 <= time.length <= 60000

1 <= time[i] <= 500

Solution:

using System;
using System.Collections.Generic;
using System.Text;

namespace LeetCode.AskGif.Easy.Array
{
 public class NumPairsDivisibleBy60Soln
 {
 public int NumPairsDivisibleBy60(int[] time)
 {
 var map = new Dictionary<int, int>();
 int count = 0;
 int val = 0;
 int diff = 0;
 for (int i = 0; i < time.Length; i++)
 {
 val = time[i] % 60;
 diff = (60 - val) % 60;
 if (map.ContainsKey(diff))
 {
 count += map[diff];
 }

 if (map.ContainsKey(val))
 {
 map[val]++;
 }
 else
 {
 map.Add(val, 1);
 }
 }

 return count;
 }
 }
}

Time Complexity: O(n)

Space Complexity: O(n)

Unit Tests:

using LeetCode.AskGif.Easy.Array;
using Microsoft.VisualStudio.TestTools.UnitTesting;
using System;
using System.Collections.Generic;
using System.Text;

namespace CodingUnitTest.Easy.Array
{
 [TestClass]
 public class NumPairsDivisibleBy60SolnTests
 {
 [TestMethod]
 public void NumPairsDivisibleBy60Soln_First()
 {
 var arr = new int[] { 30, 20, 150, 100, 40 };
 var expected = 3;

 var res = new NumPairsDivisibleBy60Soln().NumPairsDivisibleBy60(arr);
 Assert.AreEqual(expected, res);
 }

 [TestMethod]
 public void NumPairsDivisibleBy60Soln_Second()
 {
 var arr = new int[] { 60, 60, 60 };
 var expected = 3;

 var res = new NumPairsDivisibleBy60Soln().NumPairsDivisibleBy60(arr);
 Assert.AreEqual(expected, res);
 }
 }
}