Intersection of Two Linked Lists

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.
• 统计长度，减少内存空间

1. ListNode *getIntersectionNode(ListNode *headA, ListNode *headB) {
3. if(headA == NULL) return NULL;
4. if(headB == NULL) return NULL;
5. int lenA = 1;
6. int lenB = 1;
7. ListNode *pA = headA;
8. ListNode *pB = headB;
9. while(pA->next != NULL) {
10. lenA++;
11. pA=pA->next;
12. }
13. while(pB->next!=NULL) {
14. lenB++;
15. pB=pB->next;
16. }
17. if(pA!=pB) return NULL;
18. int len = max(lenA,lenB) - min(lenA,lenB);
19. pA = headA;
20. pB = headB;
21. if(lenA>lenB) {
22. while(len>0) {
23. pA = pA->next;
24. len--;
25. }
26. } else if(lenB > lenA){
27. while(len>0) {
28. pB = pB -> next;
29. len--;
30. }
31. }
32. while(pA!=pB) {
33. pA = pA->next;
34. pB = pB ->next;
35. }
36. return pA;
37. }