Fix array queue.

codes/c/chapter_stack_and_queue/array_queue.c

@@ -8,10 +8,10 @@
 
 /* 基于环形数组形成的队列 */
 struct ArrayQueue {
-    int *nums;    // 用于存储队列元素的数组
-    int cap;      // 队列容量
-    int front;    // 头指针，指向队首
-    int rear;     // 尾指针，指向队尾 + 1
+    int *nums;       // 用于存储队列元素的数组
+    int front;       // 队首指针，指向队首元素
+    int queSize;     // 尾指针，指向队尾 + 1
+    int queCapacity; // 队列容量
 };
 
 typedef struct ArrayQueue ArrayQueue;
@@ -20,33 +20,31 @@ typedef struct ArrayQueue ArrayQueue;
 ArrayQueue *newArrayQueue(int capacity) {
     ArrayQueue *queue = (ArrayQueue *) malloc(sizeof(ArrayQueue));
     // 初始化数组
-    queue->cap = capacity;
-    queue->nums = (int *) malloc(sizeof(int) * queue->cap);
-    queue->front = 0;
-    queue->rear = 0;
+    queue->queCapacity = capacity;
+    queue->nums = (int *) malloc(sizeof(int) * queue->queCapacity);
+    queue->front = queue->queSize = 0;
     return queue;
 }
 
 /* 析构函数 */
 void delArrayQueue(ArrayQueue *queue) {
     free(queue->nums);
-    queue->cap = 0;
+    queue->queCapacity = 0;
 }
 
 /* 获取队列的容量 */
 int capacity(ArrayQueue *queue) {
-    return queue->cap;
+    return queue->queCapacity;
 }
 
 /* 获取队列的长度 */
 int size(ArrayQueue *queue) {
-    // 由于将数组看作环形队列，可能 rear < front，因此需要取余数
-    return (capacity(queue) + queue->rear - queue->front) % capacity(queue);
+    return queue->queSize;
 }
 
 /* 判断队列是否为空 */
 bool empty(ArrayQueue *queue) {
-    return queue->rear - queue->front == 0;
+    return queue->queSize == 0;
 }
 
 /* 访问队首元素 */
@@ -61,26 +59,30 @@ void offer(ArrayQueue *queue, int num) {
         printf("队列已满\r\n");
         return;
     }
-    queue->nums[queue->rear] = num;
-    queue->rear = (queue->rear + 1) % capacity(queue);
+    // 计算队尾指针，指向队尾索引 + 1
+    // 通过取余操作，实现 rear 越过数组尾部后回到头部
+    int rear = (queue->front + queue->queSize) % queue->queCapacity;
+    // 尾结点后添加 num
+    queue->nums[rear] = num;
+    queue->queSize++;
 }
 
 /*  出队 */
 void poll(ArrayQueue *queue) {
     int num = peek(queue);
-    queue->front = (queue->front + 1) % capacity(queue);
+    // 队首指针向后移动一位，若越过尾部则返回到数组头部
+    queue->front = (queue->front + 1) % queue->queCapacity;
+    queue->queSize--;
 }
 
 /* 打印基于环形数组形成的队列 */
 void printArrayQueue(ArrayQueue *queue) {
-    int siz = size(queue);
-    int cap = capacity(queue);
-    int arr[siz];
+    int arr[queue->queSize];
     // 拷贝
-    for (int i = 0, j = queue->front; i < siz; i++, j++) {
-        arr[i] = queue->nums[j % cap];
+    for (int i = 0, j = queue->front; i < queue->queSize; i++, j++) {
+        arr[i] = queue->nums[j % queue->queCapacity];
     }
-    printArray(arr, siz);
+    printArray(arr, queue->queSize);
 }