A singly linked listSingly Linked ListA chain of nodes where each node stores a value and a pointer (next) to the following node. The last node's next is null. Unlike an array, nodes aren't stored contiguously in memory — the only way to reach a given node is by following next pointers from the head. is built one node at a time, connected only through each node's next pointer. Given an array of integers vals, build a singly linked list containing those values in the same order, and return its head. Each node in the list is a Node with two fields: val (the stored integer) and next (a pointer to the following node, or null if it's the last one). If vals is empty, return null — an empty list has no head.