Data Structures and Algorithms: Linked Lists in C, Slides of Data Structures and Algorithms

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Data Structures and Algorithms!

The material for this lecture is drawn, in part, from!

The Practice of Programming (Kernighan & Pike) Chapter 2!

Jennifer Rexford!

Motivating Quotations!

“Every program depends on algorithms and data

structures, but few programs depend on the

invention of brand new ones.”!

-- Kernighan & Pike!

“I will, in fact, claim that the difference between a

bad programmer and a good one is whether he

considers his code or his data structures more

important. Bad programmers worry about the

code. Good programmers worry about data

structures and their relationships.”!

-- Linus Torvalds!

A Common Task!

• Maintain a table of key/value pairs!

• Each key is a string; each value is an int

• Unknown number of key-value pairs!

• Examples!

• (student name, grade)!

• (“john smith”, 84), (“jane doe”, 93), (“bill clinton”, 81)!

• (baseball player, number)!

• (“Ruth”, 3), (“Gehrig”, 4), (“Mantle”, 7)!

• (variable name, value)!

• (“maxLength”, 2000), (“i”, 7), (“j”, -10)!

• For simplicity, allow duplicate keys (client responsibility)!

• In Assignment #3, must check for duplicate keys!!

Data Structures and Algorithms!

• Data structures!

• Linked list of key/value pairs!

• Hash table of key/value pairs!

• Algorithms!

• Create: Create the data structure!

• Add: Add a key/value pair!

• Search: Search for a key/value pair, by key!

• Free: Free the data structure!

Linked List: Data Structure!

struct Node { const char *key; int value; struct Node *next; }; struct Table { struct Node *first; }; 4 "Gehrig" 3 "Ruth" NULL

struct!

Table!

struct!

Node!

struct!

Node!

Linked List: Create (1)!

t! struct Table *Table_create(void) { struct Table t; t = (struct Table) malloc(sizeof(struct Table)); t->first = NULL; return t; } struct Table *t; … t = Table_create(); …

Linked List: Add (1)!

void Table_add(struct Table *t, const char *key, int value) { struct Node p = (struct Node)malloc(sizeof(struct Node)); p->key = key; p->value = value; p->next = t->first; t->first = p; } struct Table *t; … Table_add(t, "Ruth", 3); Table_add(t, "Gehrig", 4); Table_add(t, "Mantle", 7); … These are pointers to! strings! 4 "Gehrig" 3 "Ruth" NULL t!

Linked List: Add (2)!

void Table_add(struct Table *t, const char *key, int value) { struct Node p = (struct Node)malloc(sizeof(struct Node)); p->key = key; p->value = value; p->next = t->first; t->first = p; } struct Table *t; … Table_add(t, "Ruth", 3); Table_add(t, "Gehrig", 4); Table_add(t, "Mantle", 7); … 4 "Gehrig" 3 "Ruth" NULL t! p!

Linked List: Add (4)!

void Table_add(struct Table *t, const char *key, int value) { struct Node p = (struct Node)malloc(sizeof(struct Node)); p->key = key; p->value = value; p->next = t->first; t->first = p; } struct Table *t; … Table_add(t, "Ruth", 3); Table_add(t, "Gehrig", 4); Table_add(t, "Mantle", 7); … 4 "Gehrig" 3 "Ruth" NULL

"Mantle" t! p!

Linked List: Add (5)!

void Table_add(struct Table *t, const char *key, int value) { struct Node p = (struct Node)malloc(sizeof(struct Node)); p->key = key; p->value = value; p->next = t->first; t->first = p; } struct Table *t; … Table_add(t, "Ruth", 3); Table_add(t, "Gehrig", 4); Table_add(t, "Mantle", 7); … 4 "Gehrig" 3 "Ruth" NULL

"Mantle" t! p!

Linked List: Search (2)!

int Table_search(struct Table *t, const char *key, int *value) { struct Node *p; for (p = t->first; p != NULL; p = p->next) if (strcmp(p->key, key) == 0) { *value = p->value; return 1; } return 0; } struct Table *t; int value; int found; … found = Table_search(t, "Gehrig", &value); … t! 4 "Gehrig" 3 "Ruth" NULL

"Mantle" p!

Linked List: Search (3)!

int Table_search(struct Table *t, const char *key, int *value) { struct Node *p; for (p = t->first; p != NULL; p = p->next) if (strcmp(p->key, key) == 0) { *value = p->value; return 1; } return 0; } struct Table *t; int value; int found; … found = Table_search(t, "Gehrig", &value); … t! 4 "Gehrig" 3 "Ruth" NULL

"Mantle" p!

Linked List: Search (5)!

int Table_search(struct Table *t, const char *key, int *value) { struct Node *p; for (p = t->first; p != NULL; p = p->next) if (strcmp(p->key, key) == 0) { *value = p->value; return 1; } return 0; } struct Table *t; int value; int found; … found = Table_search(t, "Gehrig", &value); … t! 4 "Gehrig" 3 "Ruth" NULL

"Mantle" p!

Linked List: Search (6)!

int Table_search(struct Table *t, const char *key, int *value) { struct Node *p; for (p = t->first; p != NULL; p = p->next) if (strcmp(p->key, key) == 0) { *value = p->value; return 1; } return 0; } struct Table *t; int value; int found; … found = Table_search(t, "Gehrig", &value); … t! 4 "Gehrig" 3 "Ruth" NULL

"Mantle" p! 4