LeetCode 160 Intersection of Two Linked Lists（链表）

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.

题目大意：给出两个在某个节点相交的单链表，返回第一个相交节点的指针。

解题思路：设置两个指针p1和p2分别指向headA和headB，然后移动p1和p2。若p1为空，使p1指向headB；若p2为空则使p2指向headA，重复上述过程直到p1 == p2。

代码如下：

/** * Definition for singly-linked list. * struct ListNode { *     int val; *     struct ListNode *next; * }; */ struct ListNode *getIntersectionNode(struct ListNode *headA, struct ListNode *headB) {    struct ListNode *p1;    struct ListNode *p2;    p1 = headA;    p2 = headB;    if(p1 == NULL || p2 == NULL) return NULL;    while(p1 != p2){        p1 = p1->next;        p2 = p2->next;        if(p1 == p2)   return p1;        if(p1 == NULL) p1 = headB;        if(p2 == NULL) p2 = headA;    }    return p1;}