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#include <cgreen/cgreen.h>
/*
Implement the stack methods using two queues
* `push(x)`
* `pop()`
Analyze the running time of the `push(x)` and `pop()` operations based on this implementation.
*/
struct node {
int data;
struct node *next;
};
typedef struct node Node;
typedef struct {
Node *head;
int size;
} Queue;
typedef struct {
Queue *q1;
} Stack;
static Queue *newQueue(){
Queue *queue = malloc(sizeof(Queue));
queue->size = 0;
queue->head = NULL;
return queue;
}
static Stack *initialize() {
Stack *stack = malloc(sizeof(Stack));
stack->q1 = newQueue();
return stack;
}
Node *newNode(int data) {
Node *node = malloc(sizeof(Node));
node->data = data;
node->next = NULL;
return node;
}
void enqueue(Queue *q, int data) {
Node *node = newNode(data);
q->size++;
if (q->head == NULL) {
q->head = node;
} else {
Node *tail = q->head;
while (tail->next != NULL)
tail = tail->next;
tail->next = node;
}
}
int dequeue(Queue *q) {
if (q->head == NULL) return -1;
Node *node = q->head;
int data = node->data;
q->head = node->next;
free(node);
return data;
}
// The running time is linear time.
static void push(Stack *stack, int data) {
enqueue(stack->q1, data);
}
// The running time is linear time.
static int pop(Stack *stack) {
int count = stack->q1->size - 1;
Queue *tmp = newQueue();
for (int i = 0; i < count; i++)
enqueue(tmp, dequeue(stack->q1));
int data = dequeue(stack->q1);
free(stack->q1);
stack->q1 = tmp;
return data;
}
int size(Stack *stack) {
return stack->q1->size;
}
static void destroy(Stack *stack) {
int count = size(stack);
for (int i = 0; i < count; i++)
pop(stack);
free(stack->q1);
free(stack);
}
static void inspect(Queue *q) {
Node *tmp = q->head;
if (q->size == 0) {
printf("[]\n");
return;
}
printf("[");
for (int i = 0; i < q->size; i++) {
printf("%d,", tmp->data);
tmp = tmp->next;
}
printf("\b]\n");
}
Describe(Stack);
BeforeEach(Stack){ }
AfterEach(Stack){ }
Ensure(Stack, push_onto_stack) {
Stack *stack = initialize();
push(stack, 1);
assert_that(size(stack), is_equal_to(1));
push(stack, 2);
assert_that(size(stack), is_equal_to(2));
destroy(stack);
}
Ensure(Stack, pop_single_item) {
Stack *stack = initialize();
push(stack, 1);
assert_that(pop(stack), is_equal_to(1));
destroy(stack);
}
Ensure(Stack, pop_successive_items) {
Stack *stack = initialize();
push(stack, 1);
push(stack, 2);
assert_that(pop(stack), is_equal_to(2));
assert_that(pop(stack), is_equal_to(1));
destroy(stack);
}
TestSuite *stack_tests() {
TestSuite *suite = create_test_suite();
add_test_with_context(suite, Stack, push_onto_stack);
add_test_with_context(suite, Stack, pop_single_item);
add_test_with_context(suite, Stack, pop_successive_items);
return suite;
}
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