两个单向链表，找出它们的第一个公共结点

package structure.list;

import structure.list.node.LNode_01;

/**
* 题目：两个单向链表，找出它们的第一个公共结点
*
* @author Toy
*
*/
public class First_CommonNode {

LNode_01 head1 = null;
LNode_01 head2 = null;
LNode_01 head = null;

public LNode_01 method_01() {

init();

return getFirstCommonNode_01(head1, head2);
}

/**
* 逐个考察 O(m*n)
*
* @param head1
* @param head2
* @return
*/
private LNode_01 getFirstCommonNode_01(LNode_01 head1, LNode_01 head2) {

LNode_01 p = head1;
LNode_01 q = head2;

while (p != null) {
q = head2;
while (q != null) {
if (q == p) {
return p;
}
q = q.next;
}
p = p.next;
}
return null;
}

public LNode_01 method_02() {
return getFirstCommonNode_02(head1, head2);
}

/**
* 先找到长度差K，然后长的先遍历K步,二者再同步遍历
*
* @param head1
* @param head2
* @return
*/
private LNode_01 getFirstCommonNode_02(LNode_01 head1, LNode_01 head2) {
int len1 = LinkList_01.getLength(head1);
int len2 = LinkList_01.getLength(head2);
int delta = Math.abs(len1 - len2);

LNode_01 first = head1;
LNode_01 follow = head2;
if (len2 > len1) {
first = head2;
follow = head1;
}
first = LinkList_01.toNodeK(first, delta + 1);

while (follow != null && first != null) {
if (follow == first) {
return follow;
}
follow = follow.next;
first = first.next;
}

return null;
}

public void init() {
head = creatList();
head1 = creatList();
head2 = creatList();
head1 = concatList(head1, head);
head2 = concatList(head2, head);
}

private LNode_01 creatList() {
System.out.println("Creat new list");
LinkList_01 list = new LinkList_01();
list.header = null;
list.creat();
list.show();
return list.header;
}

public LNode_01 concatList(LNode_01 head1, LNode_01 head) {
LNode_01 p = head1;
while (p.next != null) {
p = p.next;
}
p.next = head;
return head1;
}

/**
* @param args
*/
public static void main(String[] args) {
First_CommonNode f = new First_CommonNode();
LNode_01 n = f.method_01();
if (n == null) {
System.out.println("not find");
} else {
System.out.println("first common elem: " + n.data);
}

n = f.method_02();
if (n == null) {
System.out.println("not find");
} else {
System.out.println("first common elem: " + n.data);
}
}

}