代码

#include <algorithm>

void sort(unsigned *a, int n) {
    if (n <= 1) return;
    
    unsigned *tmp = new unsigned[n];
    unsigned *src = a;
    unsigned *dst = tmp;
    
    // 对4个字节分别处理
    for (int shift = 0; shift < 32; shift += 8) {
        int count[256] = {0};
        
        // 统计
        for (int i = 0; i < n; i++) {
            count[(src[i] >> shift) & 0xFF]++;
        }
        
        // 前缀和
        int sum = 0;
        for (int i = 0; i < 256; i++) {
            int temp = count[i];
            count[i] = sum;
            sum += temp;
        }
        
        // 分发
        for (int i = 0; i < n; i++) {
            int idx = (src[i] >> shift) & 0xFF;
            dst[count[idx]++] = src[i];
        }
        
        // 交换指针
        unsigned *tempPtr = src;
        src = dst;
        dst = tempPtr;
    }
    
    // 如果最后数据在tmp中，复制回a
    if (src != a) {
        for (int i = 0; i < n; i++) {
            a[i] = src[i];
        }
    }
    
    delete[] tmp;
}

评测结果