Which one of the following codes can find if a linked list has a loop?

a.

Function(Cell: sentinel) Boolean: has_loop = false Cell: cell = sentinel While (cell.Next != null) If (cell.Next.Visited) cell.Next = null has_loop = true End If cell = cell.Next cell.Visited = true End While cell = sentinel While (cell.Next != null) cell.Visited = false cell = cell.Next End While Return has_loop End Function

b.

Function(Cell: sentinel) Boolean: has_loop = false Cell: cell = sentinel While (cell.Next != null) If (cell.Next.Visited) cell.Next = null has_loop = true End If cell = cell.Next cell.Visited = true End While cell = sentinel While (cell.Next != null) cell.Visited = true cell = cell.Next End While Return has_loop End Function

c.

Function(Cell: sentinel) Boolean: has_loop = false Cell: cell = sentinel While (cell.Next != null) If (cell.Next.Visited) cell.Next = null has_loop = true End If cell = cell.Next cell.Visited = false End While cell = sentinel While (cell.Next != null) cell.Visited = false cell = cell.Next End While Return has_loop End Function

d.

Function(Cell: sentinel) Boolean: has_loop = true Cell: cell = sentinel While (cell.Next != null) If (cell.Next.Visited) cell.Next = null has_loop = true End If cell = cell.Next cell.Visited = true End While cell = sentinel While (cell.Next != null) cell.Visited = false cell = cell.Next End While Return has_loop End Function