從N個數中選取最大的前10個[堆排序版]

題目:

從N個數中選取最大的前10個, 有序輸出.

N最大可能達到1000億

每個數範圍是0 - 2147483647

堆排序版測試結果:

總計[1000000]個輸入
總計比較[4232804]次
總計寫內存[3849024]次
總計耗時[0.046478s]

/* 

 * author: goosman.lei

 * mail: [email protected]

 * blog: http://blog.csdn.net/lgg201

 */

#include <stdio.h>
#include <time.h>
#include <stdlib.h>
#include <unistd.h>
#include <strings.h>

#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. 生成測試數據: %s <number> /* 標準錯誤以二進制方式輸出測試數據, 標準輸出以文本方式輸出測試數據用於腳本校驗 */\n\t2. 執行Top 10查找: %s <exec> /* 標準輸出輸出前10個最大數據(倒序), 開啓INFO時在標準錯誤輸出統計信息, 開啓DEBUG時在標準錯誤輸出調試信息\n", 
			argv[0], argv[0]);
		return (0);
	}
	if ( strcmp(argv[1], "exec") != 0 ) {
		/* 不考慮數字輸入的容錯了 */
		generate_test_data(atoi(argv[1]));
		return 0;
	}

	sbuff	= malloc(1024 * 1024 * 4 - 4);
	rbuff	= malloc(256 * 1024 * 10 * 4);	/* 足夠10000億數據 */
	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, "總計[%d]個輸入\n總計比較[%d]次\n總計寫內存[%d]次\n總計耗時[%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;
}