Intersection of Two Linked Lists

题目描述

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.

题目出处：https://oj.leetcode.com/problems/intersection-of-two-linked-lists/

解题思路

1. 首先扫描两个链表，找出长度较小的链表。
2. 将长度较长的链表多出的节点删除（从队首开始删除），然后将两个链表相同位置的元素依次比较，直到最后。
3. 只有相等，且result节点不为空，才更新result节点。

自己的源代码

package leetcode;public class IntersectionOfTwoLinkedLists {    public static ListNode getIntersectionNode(ListNode headA, ListNode headB) {    //处理链表为空的情况    if(headA==null || headB==null) return null;        //扫描链表A和B，得到链表的长度    int aLen = 0;    ListNode headATemp = headA;    while(headATemp != null){    aLen++;    headATemp = headATemp.next;    }    int bLen = 0;    ListNode headBTemp = headB;    while(headBTemp != null){    bLen++;    headBTemp = headBTemp.next;    }    //保证headA是长度较短的链表    if(aLen > bLen){    ListNode tempNode = headA;    headA = headB;    headB = tempNode;    int temp = aLen;    aLen = bLen;    bLen = temp;    }        ListNode resultNode = null;    for(int i = 0; i < bLen-aLen; i++){//删除长链表队首元素，使两个链表长度一致    headB = headB.next;    }    for(int i = 0; i < aLen; i++, headA = headA.next, headB = headB.next){    if(headA.val == headB.val) {    if(resultNode == null)//相等且为空才放入    resultNode = headA;    }    else resultNode = null;    }            return resultNode;    }    public static void main(String[] args) {ListNode head1 = new ListNode(1);ListNode head2 = new ListNode(2);ListNode head3 = new ListNode(3);ListNode head4 = new ListNode(4);ListNode head5 = new ListNode(5);ListNode head6 = new ListNode(6);ListNode head7 = new ListNode(7);ListNode head8 = new ListNode(8);head1.next = head2;head2.next = head3;head3.next = head4;head4.next = head5;head6.next = head7;head7.next = head8;head8.next = head3;ListNode headA = head1;ListNode headB = head6;IntersectionOfTwoLinkedLists.getIntersectionNode(headA, headB).print();}}