JavaScript Algorithms Online Test

A playlist is considered a repeating playlist if any of the songs contain a reference to a previous song in the playlist. Otherwise, the playlist will end with the last song which points to undefined.

Implement the method isRepeatingPlaylist that, efficiently with respect to time used, returns true if a playlist is repeating or false if it is not.

For example, the following code prints "true" as both songs point to each other.

let first = new Song("Hello");
let second = new Song("Eye of the tiger");

first.nextSong = second;
second.nextSong = first;

console.log(first.isRepeatingPlaylist());

Write a function that, when passed an array and a target sum, returns, efficiently with respect to time used, two distinct zero-based indices of any two of the numbers, whose sum is equal to the target sum. If there are no two numbers, the function should return null.

For example, findTwoSum([ 3, 1, 5, 7, 5, 9 ], 10) should return an array containing any of the following pairs of indices:

• 0 and 3 (or 3 and 0) as 3 + 7 = 10
• 1 and 5 (or 5 and 1) as 1 + 9 = 10
• 2 and 4 (or 4 and 2) as 5 + 5 = 10