SLIDE 1
Dynamic Arrays Revisited
- Dynamic array can sometimes be slow
CS261 Data Structures Linked Lists - Introduction Dynamic Arrays - - PowerPoint PPT Presentation
CS261 Data Structures Linked Lists - Introduction Dynamic Arrays - - PowerPoint PPT Presentation
CS261 Data Structures Linked Lists - Introduction Dynamic Arrays Revisited Dynamic array can sometimes be slow When? Why? Linked Lists to the Rescue Dynamic Array Linked List in memory in memory da LL Alan Newell data head a
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SLIDE 3
Linked Lists to the Rescue
Alan Newell 1956 b c Dynamic Array in memory data Size = 3 Capacity = 5 da a c b Linked List in memory head Size = 3 LL
a
What can we now do…and not do …quickly?
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- Data elements held in structures called “links”
- Like a chain: each link is tied to the next
- Links are 1 – 1 with elements, allocated and
released as necessary
data link data link … next link next link
Linked Lists - Characteristics
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struct Link { /* Single link. */ TYPE val; /* Data contained by this link. */ struct Link *next; /* Pointer to next link. */ };
val next
Typical Link Structure (Singly Linked)
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All linked lists consists of links … but there are
- ther design decisions:
– Header (special value to point to start) or no header? – Use null as terminator, or special value (sentinel) for end? – Use single or double links? – Pointer to first element only, or pointer to first and last?
Linked List Variations
Link … List Link
next
backSent frontSent
next next next prev prev prev prev next prev
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Implementing a stack interface with a linked list:
– Header with head reference only: null if empty – Null terminated – Singly linked – Where should the ‘top’ of the stack be????
- Answer: First element is easy to access
List Stack val: 2 next: val: 7 next: val: 4 next: null
Linked List Stack
firstLink
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struct linkedListStack { struct Link *firstLink; /* Initialize routine sets to zero/NULL. */ }; void linkedListStackInit (structlinkedListStack s) { s->firstLink = 0; }
Linked List Stack
List Stack
firstLink
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void pushListStack(struct ListStack *s, TYPE d) { /* You are going to write this:
- 1. Allocate (malloc) a new link (check that it works!).
*/ }
Linked List Stack
List Stack val: 2 next: val: 4 next: null
firstLink
val:? next:?
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void pushListStack(struct ListStack *s, TYPE d) { /* You are going to write this:
- 1. Allocate (malloc) a new link (check that it works!).
- 2. Set data fields in the new link.
- 3. Change head to point to new link. */
}
Linked List Stack
List Stack val: 2 next: val: 4 next: null
firstLink
val:20 next:
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void pushListStack(struct ListStack *s, TYPE d) { /* You are going to write this:
- 1. Allocate (malloc) a new link (check that it works!).
- 2. Set data fields in the new link.
- 3. Change head to point to new link. */
}
Linked List Stack
List Stack val:20 next: val: 2 next: val: 4 next: null
firstLink
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Linked List Tips…
- Draw the diagram!
- Go through the steps visually, labeling each
step
- Convert each step to C code
- Try the boundary cases:
– Empty list? – List with several items?
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- How do you tell if stack is empty?
- How do you return first element (i.e.,
firstLink)?
- How do you remove an element?
Other Linked List Operations
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- Complete Worksheet 17: Linked List
Introduction, List Stack
Your Turn
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void popListStack(struct ListStack *s, TYPE d) { struct Link *first; assert(s->firstLink); first = s->firstLink; s->firstLink = first->next; free(first); }
Linked List Stack
List Stack val:20 next: val: 2 next: val: 4 next: null
firstLink
struct ListStack { struct Link *firstLink; } struct Link { TYPE val; struct Link *next; };