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.

Credits:

Special thanks to for adding this problem and creating all test cases.

 

这道题除了阅读题目的困难较大之外， 其他的都还好。非常好做的一道题目。

代码如下：

//* 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 lengtha=1, lengthb=1;        ListNode *cora = headA, *corb = headB;        while (cora->next != NULL)        {            cora = cora->next;            lengtha++;        }        while (corb->next != NULL)        {            corb = corb->next;            lengthb++;        }        if (cora->val != corb->val)            return NULL;        int dif = lengtha - lengthb;        cora = headA, corb = headB;        if (dif >= 0)        {            while (dif)            {                dif--;                cora = cora->next;            }        }        else

{            while (dif)            {                dif++;                corb = corb->next;            }        }        while (cora != NULL)        {            if (cora == corb)                return cora;            else            {                cora = cora->next;                corb = corb->next;            }        }    }};