leetcode - Intersection of Two Linked Lists

 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 == NULL || headB == NULL){
13             return NULL;
14         }
15         ListNode *tpA = headA;
16         ListNode *tpB = headB;
17         int numA=0,numB=0;
18         while(tpA != NULL){
19             tpA = tpA->next;
20             numA++;
21         }
22         while(tpB != NULL){
23             tpB = tpB->next;
24             numB++;
25         }
26         tpA = headA;
27         tpB = headB;
28         if(numA!=numB){
29             if(numA>numB){
30                 for( int i = 0; i<(numA-numB); i++){
31                     tpA = tpA->next;
32                 }
33             }
34             else{
35                 for( int i = 0; i<(numB-numA); i++){
36                     tpB = tpB->next;
37                 }
38             }
39         }
40         while(tpA != NULL){
41             if(tpA == tpB){
42                 return tpA;
43             }
44             else{
45                 tpA = tpA->next;
46                 tpB = tpB->next;
47             }
48         }
49         return NULL;
50     }
51 };