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hash-table.c
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hash-table.c
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#include <assert.h>
#include <stdbool.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
typedef struct Item {
char *key;
int value;
struct Item *next;
} Item;
static Item *newItem(char *key, int value) {
Item *ptr = malloc(sizeof(Item));
ptr->key = key;
ptr->value = value;
ptr->next = NULL;
return ptr;
}
/**
* A hash table data structure. Will hash string keys deterministically to
* numerical indices (using an admittedly naive hashing function) and store key-
* value pairs at those hashed indices to provide more efficient lookup times.
* This implementation will handle collisions by simply storing multiple key-
* value pairs at the same hashed index in a linked list structure.
*/
typedef struct HashTable {
int numBuckets;
int length;
Item **array;
} HashTable;
HashTable *newHashTable(int numBuckets) {
if (numBuckets < 1) {
printf("Error: number of buckets must be positive.\n");
return NULL;
}
HashTable *ptr = malloc(sizeof(HashTable));
ptr->numBuckets = numBuckets;
ptr->length = 0;
ptr->array = calloc(numBuckets, sizeof(Item *));
return ptr;
}
static int hash(char *string, int size) {
int hashed = 0;
for (int i = 0; string[i]; i++) {
hashed += string[i];
}
return hashed % size;
}
/** Returns the number of items in a hash table. */
int size(HashTable *table) { return table->length; }
/** Returns whether or not a hash table is empty. */
bool isEmpty(HashTable *table) { return size(table) == 0; }
/**
* Adds a key-value pair to a hash table, overwriting a matching key if one is
* already present in the table.
*/
void set(HashTable *table, char *key, int value) {
int index = hash(key, table->numBuckets);
if (table->array[index]) {
Item *currentItem = table->array[index];
while (currentItem) {
if (strcmp(currentItem->key, key) == 0) {
// Matching key is present; overwrite existing value
currentItem->value = value;
break;
}
if (!currentItem->next) {
// Add new key-value item
currentItem->next = newItem(key, value);
table->length++;
break;
}
currentItem = currentItem->next;
}
} else {
// Add new key-value item
table->array[index] = newItem(key, value);
table->length++;
}
}
/**
* Retrieves a given key's associated value in a hash table.
*
* @param table A pointer to the hash table.
* @param key The key to search for.
* @return A pointer to the key's associated value (or `NULL` if the key is not
* present in the table).
*/
int *get(HashTable *table, char *key) {
int index = hash(key, table->numBuckets);
Item *currentItem = table->array[index];
while (currentItem) {
if (strcmp(currentItem->key, key) == 0) {
return ¤tItem->value;
}
currentItem = currentItem->next;
}
// Key was not found
return NULL;
}
/** Checks whether or not a hash table contains a given key. */
bool has(HashTable *table, char *key) {
int index = hash(key, table->numBuckets);
Item *currentItem = table->array[index];
while (currentItem) {
if (strcmp(currentItem->key, key) == 0) {
return true;
}
currentItem = currentItem->next;
}
// Key was not found
return false;
}
/**
* Given a key, removes its key-value pair from a hash table (if present).
*
* @param table A pointer to the hash table.
* @param key The key to remove.
* @return `0` if a key-value pair was removed, `1` if the key was not present
* in the table.
*/
int del(HashTable *table, char *key) {
int index = hash(key, table->numBuckets);
if (!table->array[index])
return 1;
if (strcmp(table->array[index]->key, key) == 0) {
Item *deletedItem = table->array[index];
table->array[index] = table->array[index]->next;
table->length--;
free(deletedItem);
return 0;
}
Item *previousItem = table->array[index];
Item *currentItem = table->array[index]->next;
while (currentItem) {
if (strcmp(currentItem->key, key) == 0) {
previousItem->next = currentItem->next;
table->length--;
free(currentItem);
return 0;
}
previousItem = currentItem;
currentItem = currentItem->next;
}
// Key was not present
return 1;
}
/** Clears the contents of a hash table. */
void clear(HashTable *table) {
for (int i = 0; i < table->numBuckets; i++) {
Item *currentItem = table->array[i];
while (currentItem) {
Item *nextItem = currentItem->next;
free(currentItem);
currentItem = nextItem;
}
table->array[i] = NULL;
}
table->length = 0;
}
/**
* Frees the allocated memory for a hash table, its internal array, and its
* contents.
*/
void destroy(HashTable *table) {
clear(table);
free(table->array);
free(table);
}
/**
* Returns a pointer to an array of all values in a hash table. (Make sure to
* `free` the pointer when finished with the array.)
*/
int *values(HashTable *table) {
int *valuesArray = malloc(table->length * sizeof(int));
int vIndex = 0;
for (int i = 0; i < table->numBuckets; i++) {
Item *currentItem = table->array[i];
while (currentItem) {
valuesArray[vIndex++] = currentItem->value;
currentItem = currentItem->next;
}
}
return valuesArray;
}
/**
* Prints the contents of a hash table to the console (in an arbitrary order
* determined by internal structure, not by keys, values, or insertion order).
*/
void print(HashTable *table) {
printf("{");
bool firstItemAlreadyPrinted = false;
for (int i = 0; i < table->numBuckets; i++) {
Item *currentItem = table->array[i];
while (currentItem) {
if (firstItemAlreadyPrinted) {
printf(",");
} else {
firstItemAlreadyPrinted = true;
}
printf(" \"%s\": %d", currentItem->key, currentItem->value);
currentItem = currentItem->next;
}
}
printf(" }\n");
}
int main() {
assert(newHashTable(0) == NULL);
HashTable *t = newHashTable(100);
assert(isEmpty(t));
assert(size(t) == 0);
assert(del(t, "things") == 1);
assert(!has(t, "stuff"));
print(t);
set(t, "legs", 4);
set(t, "tails", 1);
assert(*get(t, "legs") == 4);
assert(*get(t, "tails") == 1);
print(t);
set(t, "legs", 6);
assert(*get(t, "legs") == 6);
assert(has(t, "legs"));
assert(!isEmpty(t));
assert(size(t) == 2);
print(t);
int *v = values(t);
assert((v[0] == 6 && v[1] == 1) || (v[0] == 1 && v[1] == 6));
free(v);
assert(get(t, "eyes") == NULL);
assert(del(t, "tails") == 0);
assert(get(t, "tails") == NULL);
print(t);
assert(del(t, "noses") == 1);
assert(del(t, "tails") == 1);
clear(t);
assert(isEmpty(t));
assert(get(t, "legs") == NULL);
assert(!has(t, "legs"));
print(t);
destroy(t);
printf("All tests passed successfully.\n");
return 0;
}