【leetcode】Intersection of Two Linked Lists(easy)

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：简单题 遍历长度 走差值 再同步走   答案里给了个转圈圈的思路 感觉没有自己的好 太乱了

ListNode *getIntersectionNode(ListNode *headA, ListNode *headB) {

        if(headA == NULL || headB == NULL)

        {

            return NULL;

        }

        int lenA = 1;

        int lenB = 1;

        ListNode * pa = headA;

        ListNode * pb = headB;



        while(pa->next != NULL)

        {

            pa = pa->next;

            lenA++;

        }

        while(pb->next != NULL)

        {

            pb = pb->next;

            lenB++;

        }



        if(pa != pb) return NULL;



        pa = headA;

        pb = headB;

        while(lenA > lenB)

        {

            pa = pa->next; lenA--;

        }

        while(lenB > lenA)

        {

            pb = pb->next; lenB--;

        }

        while(pa != pb)

        {

            pa = pa->next;

            pb = pb->next;

        }



    }