LeetCode – Refresh – Intersection of Two Linked Lists

Find the common length part, then check with two pointers.

 1 /**
 2  * Definition for singly-linked list.
 3  * struct ListNode {
 4  *     int val;
 5  *     ListNode *next;
 6  *     ListNode(int x) : val(x), next(NULL) {}
 7  * };
 8  */
 9 class Solution {
10 public:
11     ListNode *getIntersectionNode(ListNode *headA, ListNode *headB) {
12         if (!headA || !headB) return NULL;
13         int la = 1, lb = 1;
14         ListNode *runner = headA;
15         while (runner->next) {
16             runner = runner->next;
17             la++;
18         }
19         runner = headB;
20         while (runner->next) {
21             runner = runner->next;
22             lb++;
23         }
24         if (la > lb) {
25             while (la > lb) {
26                 headA = headA->next;
27                 la--;
28             }
29         } else {
30             while (lb > la) {
31                 headB = headB->next;
32                 lb--;
33             }
34         }
35         while (headA && headA->val != headB->val) {
36             headA = headA->next;
37             headB = headB->next;
38         }
39         return headA;
40     }
41 };