[C语言][LeetCode][160]Intersection of Two Linked Lists

题目

Intersection of Two Linked Lists

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

For example, the following two linked lists:



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.

标签

Linked List

难度

简单

分析

题目意思是判断两个链表是否有交集，如果有，返回交集开始的地方。做法是先比较链表A和链表B，哪个比较长，接着长的链表先步进，走到跟短的链表起始位置一样了，然后逐个判断是否有相交的地方。

C代码实现

struct ListNode *getIntersectionNode(struct ListNode *headA, struct ListNode *headB)
{
struct ListNode *LA, *LB;
struct ListNode *h1, *h2;
int lenA=0, lenB=0, step=0;

if(!headA || !headB)
return NULL;

LA = headA;
LB = headB;

while(LA)
{
lenA++;
LA = LA->next;
}

while(LB)
{
lenB++;
LB = LB->next;
}

if(lenA >= lenB)
{
step = lenA - lenB;
h1 = headA;
h2 = headB;
}
else
{
step = lenB - lenA;
h1 = headB;
h2 = headA;
}

while(h1 && step)
{
step--;
h1 = h1->next;
}

while(h1 && h2)
{
if(h1->val == h2->val)
return h1;

h1 = h1->next;
h2 = h2->next;
}

return NULL;
}