代码

#include <string.h>
typedef unsigned int u32;
static u32 cnt[1024];
void sort(unsigned *a, int n) {
  u32 *c1 = cnt, *c2 = cnt + 256, *c3 = cnt + 512, *c4 = cnt + 768;
  memset(cnt, 0, sizeof(cnt));
  for (int i = 0; i < n; i++) {
    u32 x = a[i];
    c1[x & 255]++;
    c2[(x >> 8) & 255]++;
    c3[(x >> 16) & 255]++;
    c4[x >> 24]++;
  }
  // don't distribute (WA expected)
}

评测结果