feat(codes/c): Add linkedlist_queue.c (krahets#413)

* feat(codes/c): Add linkedlist_queue.c

* feat(codes/c): Prevent null pointer access errors in linkedlist_queue.c

* Update linkedlist_queue.c

* Update linkedlist_queue.c

---------

Co-authored-by: Yudong Jin <[email protected]>

codes/c/chapter_stack_and_queue/CMakeLists.txt

@@ -1,3 +1,4 @@
 add_executable(array_stack array_stack.c)
 add_executable(linkedlist_stack linkedlist_stack.c)
-add_executable(array_queue array_queue.c)
+add_executable(array_queue array_queue.c)
+add_executable(linkedlist_queue linkedlist_queue.c)

codes/c/chapter_stack_and_queue/linkedlist_queue.c

@@ -0,0 +1,128 @@
+/**
+ * File: linkedlist_queue.c
+ * Created Time: 2023-03-13
+ * Author: Gonglja ([email protected])
+ */
+
+#include "../include/include.h"
+
+/* 基于链表实现的队列 */
+struct LinkedListQueue {
+    ListNode *front, *rear;
+    int queSize;
+};
+
+typedef struct LinkedListQueue LinkedListQueue;
+
+/* 构造方法 */
+LinkedListQueue *newLinkedListQueue() {
+    LinkedListQueue *queue = (LinkedListQueue *) malloc(sizeof(LinkedListQueue));
+    queue->front = NULL;
+    queue->rear = NULL;
+    queue->queSize = 0;
+}
+
+/* 析构方法 */
+void delLinkedListQueue(LinkedListQueue *queue) {
+    // 释放所有结点
+    for (int i=0; i<queue->queSize && queue->front != NULL; i++) {
+        ListNode *tmp = queue->front;
+        queue->front = queue->front->next;
+        free(tmp);
+    }
+    // 释放 queue 结构体
+    free(queue);
+}
+
+/* 获取队列的长度 */
+int size(LinkedListQueue *queue) {
+    return queue->queSize;
+}
+
+/* 判断队列是否为空 */
+bool empty(LinkedListQueue *queue) {
+    return (size(queue) == 0);
+}
+
+/* 入队 */
+void push(LinkedListQueue *queue, int num) {
+    // 尾结点处添加 node 
+    ListNode *node = newListNode(num);
+    // 如果队列为空，则令头、尾结点都指向该结点
+    if (queue->front == NULL) {
+        queue->front = node;
+        queue->rear = node;
+    }  
+    // 如果队列不为空，则将该结点添加到尾结点后
+    else {
+        queue->rear->next = node;
+        queue->rear = node;
+    }
+    queue->queSize++;
+}
+
+/* 访问队首元素 */
+int peek(LinkedListQueue *queue) {
+    assert(size(queue) && queue->front);
+    return queue->front->val;
+}
+
+/* 出队 */
+void poll(LinkedListQueue *queue) {
+    int num = peek(queue);
+    ListNode *tmp = queue->front;
+    queue->front = queue->front->next;
+    free(tmp);
+    queue->queSize--;
+}
+
+/* 打印队列 */
+void printLinkedListQueue(LinkedListQueue *queue) {
+    int arr[queue->queSize];
+    // 拷贝链表中的数据到数组
+    int i;
+    ListNode *node;
+    for (i=0, node = queue->front; i < queue->queSize && queue->front != queue->rear; i++){
+        arr[i] = node->val;
+        node = node->next;
+    }
+    printArray(arr, queue->queSize);
+}
+
+/* Driver Code */
+int main() {
+    /* 初始化队列 */
+    LinkedListQueue *queue = newLinkedListQueue();
+
+    /* 元素入队 */
+    push(queue, 1);
+    push(queue, 3);
+    push(queue, 2);
+    push(queue, 5);
+    push(queue, 4);
+    printf("队列 queue = ");
+    printLinkedListQueue(queue);
+
+    /* 访问队首元素 */
+    int peekNum = peek(queue);
+    printf("队首元素 peek = %d\r\n", peekNum);
+
+    /* 元素出队 */
+    poll(queue);
+    printf("出队元素 poll = %d，出队后 queue = ", peekNum);
+    printLinkedListQueue(queue);
+
+    /* 获取队列的长度 */
+    int queueSize = size(queue);
+    printf("队列长度 size = %d\r\n", queueSize);
+
+    /* 判断队列是否为空 */
+    bool isEmpty = empty(queue);
+    printf("队列是否为空 = %s\r\n", isEmpty ? "true" : "false");
+
+    // 释放内存
+    delLinkedListQueue(queue);
+
+    return 0;
+}
+