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;	
            
        }
};