Given an array of citations (each citation is a non-negative integer) of a researcher, write a function to compute the researcher's h-index.

Ugly numbers are positive numbers whose prime factors only include 2, 3, 5. For example, 1, 2, 3, 4, 5, 6, 8, 9, 10, 12 is the sequence of the first 10 ugly numbers.

Ugly numbers are positive numbers whose prime factors only include 2, 3, 5. For example, 6, 8 are ugly while 14 is not ugly since it includes another prime factor 7.

Write a program to find the node at which the intersection of two singly linked lists begins. For example, the following two linked lists, they begin to intersect at node c1.

Given a linked list, return the node where the cycle begins. If there is no cycle, return null.