Leetcode——160. Intersection of Two Linked Lists

問題

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
           

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.

解答

第一次0ms，100%！

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/**
 * 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) {
        ListNode *p1=headA,*p2=headB;

        while(p1!=NULL&&p2!=NULL)//不同時為空
        {
            if(p1==p2) return p1;
            p1=p1->next;
            p2=p2->next;
            if(p1==NULL&&p2==NULL) return NULL;
            if(p1==NULL) p1=headB;
            if(p2==NULL) p2=headA;
        }
        return NULL;

    }
};