v0.40: Create exercises. Challenge the community.

detect_cycle

Your mission

Implement a function that decides whether a singly linked list eventually loops back onto itself or terminates with a NULL pointer.

See it in action

detect_cycle(NULL)

Expected result

Your checklist

For your own tracking. Tests grade your code.

Include list.h in your detect_cycle.c file; it defines the ListNode struct with a void *data payload and a struct ListNode *next pointer.
Return 1 as soon as you can prove that following next pointers from the head will revisit a node already seen.
Return 0 when the chain reaches NULL without ever revisiting a node.
Return 0 when the input pointer is NULL.
Use constant extra memory, the classic two-pointer (slow / fast) technique is a perfect fit.
The prototype is int detect_cycle(ListNode *list);.

More examples

detect_cycle(head) // list: A -> B -> C -> NULL

Expected result

detect_cycle(head) // list: A -> B -> C -> D -> A (tail loops to head)

Expected result

Constraints

Expected files

detect_cycle.c

Allowed functions

None. Write every helper yourself.

Allowed headers

<stddef.h>defines NULL

detect_cycle

Linked lists

Your mission

Implement a function that decides whether a singly linked list eventually loops back onto itself or terminates with a NULL pointer.

See it in action

detect_cycle(NULL)

Expected result

Your checklist

For your own tracking. Tests grade your code.

Include list.h in your detect_cycle.c file; it defines the ListNode struct with a void *data payload and a struct ListNode *next pointer.
Return 1 as soon as you can prove that following next pointers from the head will revisit a node already seen.
Return 0 when the chain reaches NULL without ever revisiting a node.
Return 0 when the input pointer is NULL.
Use constant extra memory, the classic two-pointer (slow / fast) technique is a perfect fit.
The prototype is int detect_cycle(ListNode *list);.

More examples

detect_cycle(head) // list: A -> B -> C -> NULL

Expected result

detect_cycle(head) // list: A -> B -> C -> D -> A (tail loops to head)

Expected result

Constraints

Expected files

detect_cycle.c

Allowed functions

None. Write every helper yourself.

Allowed headers

<stddef.h>defines NULL

Tests

Run the tests to grade your code

Build your code, then check each test here. Open a result to inspect its output.

Build

01NULL listWaiting

02Single node terminating in NULLWaiting

03Single node looping to itselfWaiting

04Three linear nodesWaiting

05Five nodes, tail loops to headWaiting

06Five nodes, tail loops to middleWaiting

07Eight linear nodesWaiting

detect_cycle

Your mission

Implement a function that decides whether a singly linked list eventually loops back onto itself or terminates with a NULL pointer.

See it in action

detect_cycle(NULL)

Expected result

Your checklist

For your own tracking. Tests grade your code.

Include list.h in your detect_cycle.c file; it defines the ListNode struct with a void *data payload and a struct ListNode *next pointer.
Return 1 as soon as you can prove that following next pointers from the head will revisit a node already seen.
Return 0 when the chain reaches NULL without ever revisiting a node.
Return 0 when the input pointer is NULL.
Use constant extra memory, the classic two-pointer (slow / fast) technique is a perfect fit.
The prototype is int detect_cycle(ListNode *list);.

More examples

detect_cycle(head) // list: A -> B -> C -> NULL

Expected result

detect_cycle(head) // list: A -> B -> C -> D -> A (tail loops to head)

Expected result

Constraints

Expected files

detect_cycle.c

Allowed functions

None. Write every helper yourself.

Allowed headers

<stddef.h>defines NULL

detect_cycle

Linked lists

Your mission

Implement a function that decides whether a singly linked list eventually loops back onto itself or terminates with a NULL pointer.

See it in action

detect_cycle(NULL)

Expected result

Your checklist

For your own tracking. Tests grade your code.

Include list.h in your detect_cycle.c file; it defines the ListNode struct with a void *data payload and a struct ListNode *next pointer.
Return 1 as soon as you can prove that following next pointers from the head will revisit a node already seen.
Return 0 when the chain reaches NULL without ever revisiting a node.
Return 0 when the input pointer is NULL.
Use constant extra memory, the classic two-pointer (slow / fast) technique is a perfect fit.
The prototype is int detect_cycle(ListNode *list);.

More examples

detect_cycle(head) // list: A -> B -> C -> NULL

Expected result

detect_cycle(head) // list: A -> B -> C -> D -> A (tail loops to head)

Expected result

Constraints

Expected files

detect_cycle.c

Allowed functions

None. Write every helper yourself.

Allowed headers

<stddef.h>defines NULL

Tests

Run the tests to grade your code

Build your code, then check each test here. Open a result to inspect its output.

Build

01NULL listWaiting

02Single node terminating in NULLWaiting

03Single node looping to itselfWaiting

04Three linear nodesWaiting

05Five nodes, tail loops to headWaiting

06Five nodes, tail loops to middleWaiting

07Eight linear nodesWaiting

v0.40: Create exercises. Challenge the community.

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