从N个数中选取最大的前10个[堆排序版]

题目:

从N个数中选取最大的前10个, 有序输出.

N最大可能达到1000亿

每个数范围是0 - 2147483647

堆排序版测试结果:

总计[1000000]个输入
总计比较[4232804]次
总计写内存[3849024]次
总计耗时[0.046478s]

/* 

 * author: goosman.lei

 * mail: [email protected]

 * blog: http://blog.csdn.net/lgg201

 */

#include
#include
#include
#include
#include

#define BUFF_LEN    (4096)

#define PARENT(i)   ((i) / 2 - 1)
#define LEFT(i)     ((i + 1) * 2 - 1)
#define RIGHT(i)    ((i + 1) * 2)

/* #define DEBUG */
#define INFO

#ifdef INFO
    int     s_0, s_1, s_2;
    struct timeval  begin, end;
#endif

typedef struct queue_s  queue_t;
struct queue_s {
    int     data;
    queue_t *next;
};

static void generate_test_data(long n) {
    long    i;
    int     r;
    int     l;

    l   = sizeof(int);
    srand(time(NULL));
    for ( i = 0; i < n; i ++ ) {
        r   = rand();
        fprintf(stdout, "%d\n", r);
        write(STDERR_FILENO, &r, l);
    }
}
static int read_input(int fd, void *buff, int buff_len) {
    int     i, ret;

    for ( i = 0; i < buff_len; ) {
        ret = read(fd, buff, BUFF_LEN);
        if ( -1 == ret ) {
            perror("read error\n");
            exit(0);
        } else if ( 0 == ret ) {
            break;
        } else {
            buff    += ret;
            i       += ret;
        }
    }
    return i;
}

static void dump_link(queue_t *q, int n) {
    for ( ; q != NULL; q = q->next )
        fprintf(n ? stderr : stdout, "%d\n", q->data);
    if ( n ) printf("\n");
}

void max_heapify(int *sbuff, int j) {
    int i;
#ifdef INFO
    s_0 += 3;
    s_1 ++;
#endif
    if ( sbuff[j] < sbuff[LEFT(j)] )
        i   = LEFT(j);
    else
        i   = j;
    if ( sbuff[i] < sbuff[RIGHT(j)] ) {
        i   = RIGHT(j);
#ifdef INFO
    s_1 ++;
#endif
    }
    if ( i != j ) {
        sbuff[i]    ^= sbuff[j];
        sbuff[j]    ^= sbuff[i];
        sbuff[i]    ^= sbuff[j];
        max_heapify(sbuff, i);
#ifdef INFO
    s_1 += 3;
#endif
    }
}
int main(int argc, char *argv[]) {
    int     *sbuff, *rbuff, *rbuff_t;
    int     i, j, n, rbuff_n;

    if ( argc < 2 ) {
        printf("usage: \n\t1. 生成测试数据: %s  /* 标准错误以二进制方式输出测试数据, 标准输出以文本方式输出测试数据用于脚本校验 */\n\t2. 执行Top 10查找: %s  /* 标准输出输出前10个最大数据(倒序), 开启INFO时在标准错误输出统计信息, 开启DEBUG时在标准错误输出调试信息\n",
            argv[0], argv[0]);
        return (0);
    }
    if ( strcmp(argv[1], "exec") != 0 ) {
        /* 不考虑数字输入的容错了 */
        generate_test_data(atoi(argv[1]));
        return 0;
    }

    sbuff   = malloc(1024 * 1024 * 4 - 4);
    rbuff   = malloc(256 * 1024 * 10 * 4);  /* 足够10000亿数据 */
    rbuff_t = rbuff;
    rbuff_n = 0;

#ifdef INFO
    s_0 = 0;
    s_1 = 0;
    s_2 = 0;
    gettimeofday(&begin, NULL);
#endif
    while ( 0 != (n = read_input(STDIN_FILENO, sbuff, 1024 * 1024 * 4 - 4)) ) {
#ifdef INFO
    s_2 += n / 4;
#endif
        for ( j = (n / 4) / 2; j >= 0; j -- ) {
#ifdef INFO
    s_0 ++;
#endif
            max_heapify(sbuff, j);
        }
        for ( i = 0; i < 10; i ++ ) {
#ifdef INFO
    s_0 ++;
    s_1 += 4;
#endif
            rbuff[rbuff_n]  = sbuff[0];
            sbuff[0]        = sbuff[(n / 4) - 1 - i];
            sbuff[(n / 4) - 1 - i]  = -1;
            max_heapify(sbuff, 0);
            rbuff_n ++;
        }
    }
    for ( j = rbuff_n / 2; j >= 0; j -- ) {
#ifdef INFO
    s_0 ++;
#endif
        max_heapify(rbuff, j);
    }
    for ( i = 0; i < 10; i ++ ) {
#ifdef INFO
    s_0 ++;
    s_1 += 4;
#endif
        printf("%d\n", rbuff[0]);
        rbuff[0]    = rbuff[rbuff_n - i];
        rbuff[rbuff_n - i]  = -1;
        max_heapify(rbuff, 0);
    }
#ifdef INFO
    gettimeofday(&end, NULL);
#endif

#ifdef INFO
    fprintf(stderr, "总计[%d]个输入\n总计比较[%d]次\n总计写内存[%d]次\n总计耗时[%0.6fs]\n",
        s_2, s_0, s_1, (end.tv_sec * 1000000 + end.tv_usec - begin.tv_sec * 1000000 - begin.tv_usec) / 1000000.0);
#endif

    return 0;
}