/**
* 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) {
int counta = 0, countb = 0;
ListNode * ptra = headA;
while(ptra != nullptr){
counta++;
ptra = ptra->next;
}
ListNode * ptrb = headB;
while(ptrb != nullptr){
countb++;
ptrb = ptrb->next;
}
// reset ptrb and ptra
ptrb = headB;
ptra = headA;
if (counta > countb){
int diff = counta-countb;
while(diff-- != 0)
ptra = ptra->next;
}
else {
int diff = countb-counta;
while(diff-- != 0)
ptrb = ptrb->next;
}
// begin compare
while(ptra != nullptr){
if (ptra == ptrb) return ptra;
else {
ptra = ptra->next;
ptrb = ptrb->next;
}
}
return nullptr;
}
};
The idea is to get the count first, then shift the pointers so that they start together...
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