（LeetCode）两个链表的第一个公共节点

LeetCode上面的题目例如以下：

Write a program to find the node at which the intersection of two singly linked lists begins.

For example, the following two linked lists:

A:          a1 → a2
                   ↘
                     c1 → c2 → c3
                   ↗
B:     b1 → b2 → b3

begin to intersect at node c1.

Notes:

• If the two linked lists have no intersection at all, return null.
• The linked lists must retain their original structure after the function returns.
• You may assume there are no cycles anywhere in the entire linked structure.
• Your code should preferably run in O(n) time and use only O(1) memory.

我的解决方法例如以下:

/**

 * Definition for singly-linked list.

 * public class ListNode {

 *     int val;

 *     ListNode next;

 *     ListNode(int x) {

 *         val = x;

 *         next = null;

 *     }

 * }

 */

public class Solution {

    public ListNode getIntersectionNode(ListNode headA, ListNode headB) {

        

int lengthA = 0,lengthB = 0;

for(ListNode head= headA;head!=null;head = head.next)

{

lengthA++;

}

for(ListNode head = headB;head!=null;head = head.next)

{

lengthB++;

}

if(lengthA>=lengthB)

{

for(int i=0;i<lengthA-lengthB;i++)

{

headA = headA.next;

}

}

else

{

for(int i=0;i<lengthB-lengthA;i++)

{

headB = headB.next;

}

}

for(ListNode newA =headA,newB = headB;newA!=null&&newB!=null;newA = newA.next,newB = newB.next)

{

if(newA==newB)

{

return newA;

}

}

return null;

    }

}