leetCode(3):Intersection of Two Linked Lists 分类： leetCode 2015-06-16 14:41 124人阅读 评论(0) 收藏

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.

/**
* 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;
int a=0;
int b=0;

ListNode* p=headA;
while(p)
{
a++;
p=p->next;
}
p=headB;
while(p)
{
b++;
p=p->next;
}

int diff=a-b;

ListNode* pA=headA;
ListNode* pB=headB;

if(diff>=0)
{
int i=0;
while(i<diff)
{
pA=pA->next;
i++;
}
}
else
{
diff*=(-1);
int i=0;
while(i<diff)
{
pB=pB->next;
i++;
}
}
while(pA!=pB && pA!=NULL)
{
pA=pA->next;
pB=pB->next;
}
if(pA==NULL)
return NULL;
else
return pA;

}
};