算法（二）：快速排序
（1）选择中值，根据坐标，三者取其中
（2）分别与中值比较，将数据分成两部分
（3）两部分中分别再使用同样的方法，分成更小的两部分，直到不可再分
（4）qksort中的递归，可以保证a[0]~a[j]完全排序，所以i = j+1;
代码：
root@ubuntu:/mnt/shared/appbox/qksort# cat qksort.c
#include <stdlib.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <stdio.h>
static int compare_int(const void *int1, const void *int2)
{
if(*(const int *)int1 == *(const int *)int2)
return 0;
return *(const int *)int1 > *(const int *)int2 ? 1 : -1;
}
static int get_mid_value(int *data)
{
if(compare_int(&data[0], &data[1])>0)//d[0]>d[1]
{
if(compare_int(&data[0], &data[2]) > 0)
return compare_int(&data[1], &data[2]) > 0 ? data[1] : data[2];
else
return data[0];
}
else // d[0] < d[1]
{
if(compare_int(&data[0], &data[2]) > 0)//d[0] > d[2]
return data[0]; // d[2]<d[0]<d[1], return d[0]
else//d[0] < d[2]
return compare_int(&data[1] ,&data[2]) > 0? data[2]:data[1];
}
return -1;
}
static int partition(int *a, int esize, int i, int k, int (*compare)(const void *key1, const void *key2))
{
int m;
int mid, middle;
int r[3];
int temp;
r[0] = (rand()%(k-i+1) + i);
r[1] = (rand()%(k-i+1) + i);
r[2] = (rand()%(k-i+1) + i);
mid = get_mid_value(r);
middle = a[mid];
printf("r[0]:%d, r[1]:%d, r[2]:%d, mid:%d,middle:%d\n", r[0],r[1],r[2],mid, middle);
i--;
k++;
while(1)
{
do
{
k--;
}while(compare(&a[k], &middle) > 0);
do
{
i++;
}while(compare(&a[i], &middle) < 0);
if(i>=k)
break;
else
{
temp = a[i];
a[i] = a[k];
a[k] = temp;
}
}
return k;
}
int qksort(void *data, int size, int esize, int i, int k, int (*compare)(const void *key1, const void *key2))
{
int j;
int m;
while(i < k)
{
if((j = partition(data, esize, i, k, compare)) < 0)
return -1;
if(qksort(data, size, esize, i, j, compare) < 0)
return -1;
i = j + 1;
}
return 0;
}
int main(int argc, char *argv[])
{
int ret;
int i, j, k;
i = 11;
j = 12;
int array[10]= {1,4,7,2,5,8,3,6,9,10};
printf("\n******************compare_init test**********************\n");
printf("compare_int(&i, &j)=%d\n", compare_int(&i, &j));
printf("compare_int(&j, &i)=%d\n", compare_int(&j, &i));
printf("compare_int(&i, &i)=%d\n", compare_int(&i, &i));
printf("\n******************partition test**********************\n");
qksort(array, 10, 4, 0, 9, compare_int);
for(i=0; i<10; i++)
printf("%d ", array[i]);
printf("\n");
return 0;
}
执行结果：
root@ubuntu:/mnt/shared/appbox/qksort# ./qksort
******************compare_init test**********************
compare_int(&i, &j)=-1
compare_int(&j, &i)=1
compare_int(&i, &i)=0
******************partition test**********************
r[0]:3, r[1]:6, r[2]:7, mid:6,middle:3
r[0]:1, r[1]:2, r[2]:1, mid:1,middle:3
r[0]:0, r[1]:0, r[2]:1, mid:0,middle:1
r[0]:6, r[1]:5, r[2]:8, mid:6,middle:4
r[0]:6, r[1]:5, r[2]:9, mid:6,middle:7
r[0]:5, r[1]:4, r[2]:4, mid:4,middle:5
r[0]:5, r[1]:5, r[2]:6, mid:5,middle:6
r[0]:9, r[1]:7, r[2]:7, mid:7,middle:8
r[0]:8, r[1]:8, r[2]:8, mid:8,middle:9
1 2 3 4 5 6 7 8 9 10
root@ubuntu:/mnt/shared/appbox/qksort#
增加对流程的打印：
root@ubuntu:/mnt/shared/appbox/qksort# cat qksort.c
#include <stdlib.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <stdio.h>
static int compare_int(const void *int1, const void *int2)
{
if(*(const int *)int1 == *(const int *)int2)
return 0;
return *(const int *)int1 > *(const int *)int2 ? 1 : -1;
}
static int get_mid_value(int *data)
{
if(compare_int(&data[0], &data[1])>0)//d[0]>d[1]
{
if(compare_int(&data[0], &data[2]) > 0)
return compare_int(&data[1], &data[2]) > 0 ? data[1] : data[2];
else
return data[0];
}
else // d[0] < d[1]
{
if(compare_int(&data[0], &data[2]) > 0)//d[0] > d[2]
return data[0]; // d[2]<d[0]<d[1], return d[0]
else//d[0] < d[2]
return compare_int(&data[1] ,&data[2]) > 0? data[2]:data[1];
}
return -1;
}
static int partition(int *a, int esize, int i, int k, int (*compare)(const void *key1, const void *key2))
{
int m;
int mid, middle;
int r[3];
int temp;
r[0] = (rand()%(k-i+1) + i);
r[1] = (rand()%(k-i+1) + i);
r[2] = (rand()%(k-i+1) + i);
mid = get_mid_value(r);
middle = a[mid];
printf("r[0]:%d, r[1]:%d, r[2]:%d, mid:%d,middle:%d\n", r[0],r[1],r[2],mid, middle);
i--;
k++;
while(1)
{
do
{
k--;
}while(compare(&a[k], &middle) > 0);
do
{
i++;
}while(compare(&a[i], &middle) < 0);
if(i>=k)
break;
else
{
temp = a[i];
a[i] = a[k];
a[k] = temp;
}
}
return k;
}
int qksort(void *data, int size, int esize, int i, int k, int (*compare)(const void *key1, const void *key2))
{
int j;
int m;
while(i < k)
{
printf("\n--------------------------------------------------\n");
printf("i=%d, k=%d\n", i, k);
for(m=0; m<10; m++)
printf("%d ", ((int *)data)[m]);
printf("\n");
if((j = partition(data, esize, i, k, compare)) < 0)
return -1;
printf("j=%d, a[j]:%d\n", j, ((int *)data)[j]);
for(m=0; m<10; m++)
printf("%d ", ((int *)data)[m]);
printf("\n");
if(qksort(data, size, esize, i, j, compare) < 0)
return -1;
for(m=0; m<10; m++)
printf("%d ", ((int *)data)[m]);
printf("\n");
i = j + 1;
}
return 0;
}
int main(int argc, char *argv[])
{
int ret;
int i, j, k;
i = 11;
j = 12;
int array[10]= {1,4,7,2,5,8,3,6,9,10};
printf("\n******************compare_init test**********************\n");
printf("compare_int(&i, &j)=%d\n", compare_int(&i, &j));
printf("compare_int(&j, &i)=%d\n", compare_int(&j, &i));
printf("compare_int(&i, &i)=%d\n", compare_int(&i, &i));
printf("\n******************partition test**********************\n");
qksort(array, 10, 4, 0, 9, compare_int);
for(i=0; i<10; i++)
printf("%d ", array[i]);
printf("\n");
return 0;
}
root@ubuntu:/mnt/shared/appbox/qksort#
输出：
root@ubuntu:/mnt/shared/appbox/qksort# ./qksort ******************compare_init test********************** compare_int(&i, &j)=-1 compare_int(&j, &i)=1 compare_int(&i, &i)=0 ******************partition test********************** -------------------------------------------------- i=0, k=9 1 4 7 2 5 8 3 6 9 10 r[0]:3, r[1]:6, r[2]:7, mid:6,middle:3 j=2, a[j]:2 1 3 2 7 5 8 4 6 9 10 -------------------------------------------------- i=0, k=2 1 3 2 7 5 8 4 6 9 10 r[0]:1, r[1]:2, r[2]:1, mid:1,middle:3 j=1, a[j]:2 1 2 3 7 5 8 4 6 9 10 -------------------------------------------------- i=0, k=1 1 2 3 7 5 8 4 6 9 10 r[0]:0, r[1]:0, r[2]:1, mid:0,middle:1 j=0, a[j]:1 1 2 3 7 5 8 4 6 9 10 1 2 3 7 5 8 4 6 9 10 1 2 3 7 5 8 4 6 9 10 1 2 3 7 5 8 4 6 9 10 -------------------------------------------------- i=3, k=9 1 2 3 7 5 8 4 6 9 10 r[0]:6, r[1]:5, r[2]:8, mid:6,middle:4 j=3, a[j]:4 1 2 3 4 5 8 7 6 9 10 1 2 3 4 5 8 7 6 9 10 -------------------------------------------------- i=4, k=9 1 2 3 4 5 8 7 6 9 10 r[0]:6, r[1]:5, r[2]:9, mid:6,middle:7 j=6, a[j]:7 1 2 3 4 5 6 7 8 9 10 -------------------------------------------------- i=4, k=6 1 2 3 4 5 6 7 8 9 10 r[0]:5, r[1]:4, r[2]:4, mid:4,middle:5 j=4, a[j]:5 1 2 3 4 5 6 7 8 9 10 1 2 3 4 5 6 7 8 9 10 -------------------------------------------------- i=5, k=6 1 2 3 4 5 6 7 8 9 10 r[0]:5, r[1]:5, r[2]:6, mid:5,middle:6 j=5, a[j]:6 1 2 3 4 5 6 7 8 9 10 1 2 3 4 5 6 7 8 9 10 1 2 3 4 5 6 7 8 9 10 -------------------------------------------------- i=7, k=9 1 2 3 4 5 6 7 8 9 10 r[0]:9, r[1]:7, r[2]:7, mid:7,middle:8 j=7, a[j]:8 1 2 3 4 5 6 7 8 9 10 1 2 3 4 5 6 7 8 9 10 -------------------------------------------------- i=8, k=9 1 2 3 4 5 6 7 8 9 10 r[0]:8, r[1]:8, r[2]:8, mid:8,middle:9 j=8, a[j]:9 1 2 3 4 5 6 7 8 9 10 1 2 3 4 5 6 7 8 9 10 1 2 3 4 5 6 7 8 9 10