【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;
        }

    }