折半查找，递归非递归

typedef struct node
{
    int *elem;
    int len;
} Seqlist;

int halfSearch(Seqlist list, int key) //非递归
{
    int low = 0, mid, high = list.len - 1;
    while (low <= high)
    {
        mid = high / 2;
        if (list.elem[mid] == key)
        {
            return mid;
        }
        else if (key > list.elem[mid])
        {
            low = mid + 1;
        }
        else
            high = mid - 1;
    }
    return -1;
}

int halfSearch1(Seqlist list, int key, int low, int high)
{
    int mid;
    if (low > high)
    {
        return 0;
    }
    mid = (low + high) / 2;
    if (list.elem[mid] == key)
    {
        return mid;
    }
    else if (list.elem[mid] > key)
    {
        halfSearch1(list, key, low, mid - 1);
    }
    else
        halfSearch1(list, key, mid + 1, high);
}