Find the point of intersection of two singly linked lists. Return the pointer to the node where the intersection of two lists starts.

Definition of a single linked list:

// Java
class ListNode {
  int val;
  ListNode next;
  ListNode(int x) {
    val = x;
    next = null;
  }
}

// C++
class ListNode
{
public:
  int val;
  ListNode *next;
  ListNode(int x) : val(x), next(NULL) {}
};

// C
struct ListNode
{
  int val;
  struct ListNode *next;
};

Implement a function intersection that returns a pointer to the node where the intersection of two singly linked lists starts.

// Java
ListNode intersection(ListNode l1, ListNode l2)

// C, C++
ListNode* intersection(ListNode *l1, ListNode *l2)

Example

Function intersection must return a pointer to the node with value 7.