int* maxSlidingWindow(int* nums, int numsSize, int k, int* returnSize){
    *returnSize = 0;
    if (numsSize == 0) {
        return NULL;
    }
    // 1、使用数组模拟队列
    int *queue = (int*)malloc(sizeof(int) * numsSize);
    if (queue == NULL) {
        return NULL;
    }
    memset(queue, 0, sizeof(int) * numsSize);
    // 2、对前k个元素，模拟双端队列找出第一个最大值
    int head = 0, rear = 0;
    for (int i = 0; i < k; i++) {
        while (head < rear && nums[i] > nums[queue[rear - 1]]) {
            rear--;
        }
        queue[rear++] = i;
    }
    int* res = (int*)malloc(sizeof(int) * (numsSize - k + 1));
    res[(*returnSize)++] = nums[queue[head]];
    // 3、滑动窗口，模拟双端队列找出滑动中的最大值
    for (int i = k; i < numsSize; i++) {
        // 1)窗口向前滑动，移入新数字
        while (head < rear && nums[i] > nums[queue[rear - 1]]) {
            rear--;
        }
        queue[rear++] = i;
        // 2)移出旧数字
        while (queue[head] <= i - k) {
            head++;
        }
        // 3)更新当前窗口的最大值
        res[(*returnSize)++] = nums[queue[head]];
    }
    return res;
}