两个单链表相交的问题

public static class Node {
   public int value;
   public Node next;

   public Node(int data) {
      this.value = data;
   }
}

public static Node getIntersectNode(Node head1, Node head2) {
   if (head1 == null || head2 == null) {
      return null;
   }
   Node loop1 = getLoopNode(head1);
   Node loop2 = getLoopNode(head2);
   if (loop1 == null && loop2 == null) {
      return noLoop(head1, head2);
   }
   if (loop1 != null && loop2 != null) {
      return bothLoop(head1, loop1, head2, loop2);
   }
   return null;
}


//寻找第一个入环的节点 如果有则返回  如果没有返回空
public static Node getLoopNode(Node head) {
   if (head == null || head.next == null || head.next.next == null) {
      return null;
   }
   Node n1 = head.next; // n1 -> slow
   Node n2 = head.next.next; // n2 -> fast
   while (n1 != n2) {
      if (n2.next == null || n2.next.next == null) {
         return null;
      }
      n2 = n2.next.next;
      n1 = n1.next;
   }
   n2 = head; // n2 -> walk again from head
   while (n1 != n2) {
      n1 = n1.next;
      n2 = n2.next;
   }
   return n1;
}


//没有环的情况下，起初让指针移动到距离相交节点等距的位置 然后再一起往后移动
public static Node noLoop(Node head1, Node head2) {
   if (head1 == null || head2 == null) {
      return null;
   }
   Node cur1 = head1;
   Node cur2 = head2;
   int n = 0;
   while (cur1.next != null) {
      n++;
      cur1 = cur1.next;
   }
   while (cur2.next != null) {
      n--;
      cur2 = cur2.next;
   }
   if (cur1 != cur2) {
      return null;
   }
   cur1 = n > 0 ? head1 : head2;
   cur2 = cur1 == head1 ? head2 : head1;
   n = Math.abs(n);
   while (n != 0) {
      n--;
      cur1 = cur1.next;
   }
   while (cur1 != cur2) {
      cur1 = cur1.next;
      cur2 = cur2.next;
   }
   return cur1;
}


//
public static Node bothLoop(Node head1, Node loop1, Node head2, Node loop2) {
   Node cur1 = null;
   Node cur2 = null;
   if (loop1 == loop2) {
      cur1 = head1;
      cur2 = head2;
      int n = 0;
      while (cur1 != loop1) {
         n++;
         cur1 = cur1.next;
      }
      while (cur2 != loop2) {
         n--;
         cur2 = cur2.next;
      }
      cur1 = n > 0 ? head1 : head2;
      cur2 = cur1 == head1 ? head2 : head1;
      n = Math.abs(n);
      while (n != 0) {
         n--;
         cur1 = cur1.next;
      }
      while (cur1 != cur2) {
         cur1 = cur1.next;
         cur2 = cur2.next;
      }
      return cur1;
   } else {
      cur1 = loop1.next;
      while (cur1 != loop1) {
         if (cur1 == loop2) {
            return loop1;
         }
         cur1 = cur1.next;
      }
      return null;
   }
}