Linked List Cycle — Floyds Tortoise and Hare

// C
bool hasCycle(struct ListNode *head) {
    struct ListNode *slow = head, *fast = head;
    while (fast && fast->next) {
        slow = slow->next; fast = fast->next->next;
        if (slow == fast) return true;
    }
    return false;
}

// C++
bool hasCycle(ListNode *head) {
    ListNode *slow = head, *fast = head;
    while (fast && fast->next) {
        slow = slow->next; fast = fast->next->next;
        if (slow == fast) return true;
    }
    return false;
}

// Java
public boolean hasCycle(ListNode head) {
    ListNode slow = head, fast = head;
    while (fast != null && fast.next != null) {
        slow = slow.next; fast = fast.next.next;
        if (slow == fast) return true;
    }
    return false;
}

# Python
def hasCycle(head):
    slow = fast = head
    while fast and fast.next:
        slow = slow.next
        fast = fast.next.next
        if slow is fast: return True
    return False