剑指offer 37. 两个链表的第一个公共结点

class ListNode {
int data;
ListNode next;
}

//题目：找到两个链表的第一个公共结点
public class Main {

public static void main(String[] args) throws Exception {
ListNode node1 = new ListNode();
ListNode node2 = new ListNode();
ListNode n1 = new ListNode();
ListNode n2 = new ListNode();
ListNode n3 = new ListNode();
ListNode n4 = new ListNode();
ListNode n5 = new ListNode();
node1.next = n1;
n1.next = n2;
n2.next = n4;
n4.next = n5;
node2.next = n3;
n3.next = n4;
node1.data = 1;
node2.data = 4;
n1.data = 2;
n2.data = 3;
n3.data = 5;
n4.data = 6;
n5.data = 7;
System.out.println(findFirstCommonNode(node1, node2));
}

public static ListNode findFirstCommonNode(ListNode node1, ListNode node2){
int length1 = getLength(node1);
int length2 = getLength(node2);
int diff = Math.abs(length1-length2);
if(length1>length2){											//计算出长度差diff后，将较长的链表先向后走diff步
while(diff>0){
node1 = node1.next;
diff--;
}
}else{
while(diff>0){
node2 = node2.next;
diff--;
}
}
while(node1!=null && node2!=null){
if(node1 == node2){
return node1;
}
node1 = node1.next;
node2 = node2.next;
}
return null;
}

public static int getLength(ListNode node){							//计算链表的总长度
int result = 0;
while(node!=null){
result++;
node = node.next;
}
return result;
}

}