Given a target sum and an array of positive integers, return true if any combination of numbers in the array can add to the target. Each number in the array may only be used once. Return false if the numbers cannot be used to add to the target sum.
subsetSum(2, [1, 10, 5, 3]); // false
subsetSum(10, [1, 10, 5, 3]); // true (10 === 10)
subsetSum(9, [1, 10, 5, 3]); // true (1+3+5 === 9)
Write a function that determines if a path exists between two vertices of a directed graph.
Recall that a graph is a collection of connections, or 'edges', linking together nodes or verticies. In a directed graph, each edge is like an arrow or a one-way street-- an edge linking A to B indicates that A connects to B, but not that B connects to A.
The graph passed to the function will be represented as an object with a structure sometimes called an 'adjacency list' or 'adjacency map', in which each key represents a node in the graph, and each value will consist in an array of nodes which can be reached from the key. For example, the following object:
Write a function, indexOf, which takes in two strings--the needle and the haystack--and returns the index of the first appearance of the needle in the haystack. If the needle does not appear in the haystack, return -1. Don't use indexOf(), includes() or substring(),
indexOf('or', 'hello world'); // should return 7
indexOf('hello world', 'or'); // should return -1
indexOf('howdy', 'hello world'); // should return -1