[leetcode]Intersection of Two Linked Lists

/**
* Definition for singly-linked list.
* struct ListNode {
*     int val;
*     ListNode *next;
*     ListNode(int x) : val(x), next(NULL) {}
* };
*/
class Solution {
public:
ListNode *getIntersectionNode(ListNode *headA, ListNode *headB) {
if (headA == nullptr || headB == nullptr) return nullptr;
int la = 0;
int lb = 0;
ListNode* tmpA = headA;
ListNode* tmpB = headB;
while(tmpA -> next != nullptr) {
la++;
tmpA = tmpA -> next;
}
while(tmpB -> next != nullptr) {
lb++;
tmpB = tmpB -> next;
}
if (tmpA != tmpB) return nullptr;
tmpA = headA;
tmpB = headB;

if (lb < la) {
// la must less than lb
swap(tmpA, tmpB);
swap(la, lb);
}
int diff = lb - la;
for (int i = 0; i < diff; i++) {
tmpB = tmpB -> next;
}

while (tmpA != tmpB) {
tmpA = tmpA -> next;
tmpB = tmpB -> next;
}
return tmpA;
}
};