141. Linked List Cycle, Easy
- a Must know problem
- Idea is to use two pointer, one is
slow and one is fast.
- Traverse them, one with normal rate, other one with twice the rate,
- If they match somewhere then there must be cycle, else not.
Code
```cpp
bool hasCycle(ListNode *head) {
if (!head) return false;
auto s = head;
auto f = head;
while (f -> next and f -> next -> next) {
s = s -> next;
f = f -> next -> next;
if (s == f) return true;
}
return false;
}
```