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#include <cgreen/cgreen.h>
#include <string.h>
/*
Implement the methods of the priority queue interface using a singly-linked list.
* `add(x)`
* `deleteMin()`
* `size()`
Analyze the running time of the `add(x)` and `deletMin()` operations based on this implementation.
*/
struct node {
int priority;
int data;
struct node *next;
};
typedef struct node Node;
typedef struct {
Node *head;
int size;
} PriorityQueue;
// https://en.wikipedia.org/wiki/Priority_queue
static PriorityQueue *initialize() {
PriorityQueue *queue = malloc(sizeof(PriorityQueue));
queue->size = 0;
queue->head = NULL;
return queue;
}
static Node *create_node(int priority, int data) {
Node *node = malloc(sizeof(Node));
node->priority = priority;
node->data = data;
node->next = NULL;
return node;
}
// This function is constant time O(1)
static int size(PriorityQueue *queue) {
return queue->size;
}
// This function is linear time O(n)
static void add(PriorityQueue *queue, Node *node) {
queue->size++;
if (queue->head == NULL) {
queue->head = node;
return;
}
Node *tmp = queue->head;
Node *prev = NULL;
while(tmp != NULL) {
if (tmp->data > node->data) {
node->next = tmp;
if (tmp == queue->head)
queue->head = node;
else if (prev != NULL)
prev->next = node;
break;
}
prev = tmp;
tmp = tmp->next;
}
}
// This function is constant time O(1)
static Node *delete_min(PriorityQueue *queue) {
Node *tmp = queue->head;
queue->head = tmp->next;
return tmp;
}
static void inspect(PriorityQueue *queue) {
Node *tmp = queue->head;
while(tmp) {
printf("%d\n", tmp->data);
tmp = tmp->next;
}
}
static void destroy(PriorityQueue *queue) {
Node *current = queue->head;
Node *tmp;
while(current) {
tmp = current, current = current->next;
if (tmp) free(tmp);
}
free(queue);
}
Describe(PriorityQueue);
BeforeEach(PriorityQueue){ }
AfterEach(PriorityQueue){ }
Ensure(PriorityQueue, returns_size) {
PriorityQueue *queue = initialize();
assert_that(size(queue), is_equal_to(0));
destroy(queue);
}
Ensure(PriorityQueue, adds_a_node) {
PriorityQueue *queue = initialize();
Node *node = create_node(1, 0);
add(queue, node);
assert_that(size(queue), is_equal_to(1));
destroy(queue);
}
Ensure(PriorityQueue, removes_the_node_with_the_lowest_priority){
PriorityQueue *queue = initialize();
Node *min = create_node(1, 100);
Node *mid = create_node(2, 200);
Node *max = create_node(3, 300);
add(queue, max);
add(queue, min);
add(queue, mid);
assert_that(size(queue), is_equal_to(3));
assert_that(delete_min(queue), is_equal_to(min));
assert_that(queue->head, is_equal_to(mid));
destroy(queue);
};
TestSuite *priority_queue_tests() {
TestSuite *suite = create_test_suite();
add_test_with_context(suite, PriorityQueue, returns_size);
add_test_with_context(suite, PriorityQueue, adds_a_node);
add_test_with_context(suite, PriorityQueue, removes_the_node_with_the_lowest_priority);
return suite;
}
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