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.

【思路】

无

【代码】

/**
 * 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) {
        int lena,lenb;
        lena=lenb=0;
        for(ListNode *p=headA;p!=NULL;p=p->next) lena++;
        for(ListNode *p=headB;p!=NULL;p=p->next) lenb++;
        if(lena>lenb){
            for(int i=0;i<(lena-lenb);i++) headA=headA->next;
        }
        if(lenb>lena){
            for(int i=0;i<(lenb-lena);i++) headB=headB->next;
        }
        while(headA!=headB){
            headA=headA->next;
            headB=headB->next;
        }
        return headA;
    }
};