计数排序

void counting_sort()
{
    int sorted[N];
    int maxv = a[0];
    for (int i = 1; i < n; i ++ )
        if (maxv < a[i])
            maxv = a[i];
    int count[maxv+1];
    for (int i = 0; i < n; i ++ ) count[a[i]] ++ ;
    for (int i = 1; i <= maxv; i ++ ) count[i] += count[i-1];
    for (int i = n-1; i >= 0; i -- )
    {
        sorted[count[a[i]]-1] = a[i];
        count[a[i]] -- ;
    }
    for (int i = 0; i < n; i ++ ) a[i] = sorted[i];
}