代码

#include <algorithm>
unsigned b[200000000];
unsigned buc[4][256];

void sort(unsigned *a, int n)
{
    for (int i = 0; i < n; ++i)
    {
        ++buc[0][a[i] & 255];
        ++buc[1][(a[i] >> 8) & 255];
        ++buc[2][(a[i] >> 16) & 255];
        ++buc[3][a[i] >> 24];
    }
    for (unsigned k = 0; k < 4; ++k)
    {
        unsigned offset = 0;
        for (unsigned i = 0; i < 256; ++i) 
            std::swap(buc[k][i], offset), offset += buc[k][i];
    }
    for (unsigned i = 0; i < n; ++i) b[buc[0][a[i] & 255]++] = a[i];
    for (unsigned i = 0; i < n; ++i) a[buc[1][b[i] >> 8 & 255]++] = b[i];
    for (unsigned i = 0; i < n; ++i) b[buc[2][a[i] >> 16 & 255]++] = a[i];
    for (unsigned i = 0; i < n; ++i) a[buc[3][b[i] >> 24 & 255]++] = b[i];
}

评测结果