面试题38：数字在排序数组中出现的次数

考察二分查找，找到第一个k和最后一个k，注意二分查找while (start <= end)是 <=以及如果找不到返回-1，然后再做处理

int GetFirstK(int* data, int length, int k, int start, int end)
{
    while (start <= end)
    {
        int mid = (start + end) / 2;
        if (data[mid] == k)
        {
            if (mid == 0 || data[mid - 1] != k)
                return mid;
            else
                end = mid - 1;
        }
        else if (data[mid] > k)
            end = mid - 1;
        else if(data[mid] < k)
            start = mid + 1;
    }
    return -1;
}

int GetLastK(int* data, int length, int k, int start, int end)
{
    while (start <= end)
    {
        int mid = (start + end) / 2;
        if (data[mid] == k)
        {
            if (mid == length - 1 || data[mid + 1] != k)
                return mid;
            else
                start = mid + 1;
        }
        else if (data[mid] > k)
            end = mid - 1;
        else if (data[mid] < k)
            start = mid + 1;
    }
    return -1;
}


int GetNumberOfK(int* data, int length, int k)
{
    int first = GetFirstK(data, length, k, 0, length - 1);
    int last = GetLastK(data, length, k, 0, length - 1);
    if(data == NULL || first == -1 || last == -1)
        return 0;
    else
        return last - first + 1;

}