Leetcode 160：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:

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.

class Solution {public:   ListNode *getIntersectionNode(ListNode *headA, ListNode *headB)   {    ListNode *p1 = headA;    ListNode *p2 = headB;    if (p1 == NULL || p2 == NULL) return NULL;    while (p1 != NULL && p2 != NULL && p1 != p2)     {        p1 = p1->next;        p2 = p2->next;        if (p1 == p2) return p1; //当达到相遇点时，直接返回p1或者p2        if (p1 == NULL) p1 = headB; //当p1比p2先到达结尾时，重新将其移动到第二个链表的头部        if (p2 == NULL) p2 = headA; //当p2比p1先到达结尾时，重新将其移动到第二个链表的头部，这样的话，二者到相遇点的距离是相等的    }    return p1;   }};