Intersection of Two Linked Lists——经典问题
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.
开始想道用栈来做,先入栈,然后出栈比较直接就出结果了,但是题目说只能利用一个空间,所以栈的方法不行了。
看网上的答案,没想到这么简单,暴力解法,什么算法、数据结构都没用,题刷多了,脑袋都僵了,一直以为要用什么算法来做呢。。。。
思路:
查找两个链表的第一个公共节点,如果两个节点的尾节点相同,肯定存在公共节点
方法: 长的链表开始多走 (h1的数量 - h2的数量)步,然后和短链表同步往下走,遇到的第一个相同的节点就是最早的公共节点
/**
* Definition for singly-linked list.
* struct ListNode {
* int val;
* ListNode *next;
* ListNode(int x) : val(x), next(NULL) {}
* };
*/
class Solution {
public:
ListNode *getIntersectionNode(ListNode *headA, ListNode *headB) {
if(headA==NULL||headB==NULL)
return NULL;
ListNode *flagA=headA;
ListNode *flagB=headB;
int countA=;
int countB=;
while(flagA->next!=NULL)
{
countA++;
flagA=flagA->next;
}
while(flagB->next!=NULL)
{
countB++;
flagB=flagB->next;
}
if(flagA!=flagB)
return NULL;
else
{
int diff=abs(countA- countB);
if(countA>=countB)
{
flagA=headA;
flagB=headB;
}
else
{
flagA=headB;
flagB=headA;
}
while(diff)
{
flagA=flagA->next;
diff--;
}
while(flagA!=flagB)
{
flagA=flagA->next;
flagB=flagB->next;
}
return flagA;
}
}
};
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