如何解决C中的随机排列数组
| 我正在寻找ANSI C中的一个函数，该函数可以像PHP的shuffle()
解决方法
出于持久性，从Asmodiel \的链接粘贴到Ben Pfaff的著作中：
#include <stdlib.h>
/* Arrange the N elements of ARRAY in random order.
Only effective if N is much smaller than RAND_MAX;
if this may not be the case,use a better random
number generator. */
void shuffle(int *array,size_t n)
{
if (n > 1)
{
size_t i;
for (i = 0; i < n - 1; i++)
{
size_t j = i + rand() / (RAND_MAX / (n - i) + 1);
int t = array[j];
array[j] = array[i];
array[i] = t;
}
}
}
int
struct
malloc
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <time.h>
/* compile and run with
* cc shuffle.c -o shuffle && ./shuffle */
#define NELEMS(x) (sizeof(x) / sizeof(x[0]))
/* arrange the N elements of ARRAY in random order.
* Only effective if N is much smaller than RAND_MAX;
* if this may not be the case,use a better random
* number generator. */
static void shuffle(void *array,size_t n,size_t size) {
char tmp[size];
char *arr = array;
size_t stride = size * sizeof(char);
if (n > 1) {
size_t i;
for (i = 0; i < n - 1; ++i) {
size_t rnd = (size_t) rand();
size_t j = i + rnd / (RAND_MAX / (n - i) + 1);
memcpy(tmp,arr + j * stride,size);
memcpy(arr + j * stride,arr + i * stride,size);
memcpy(arr + i * stride,tmp,size);
}
}
}
#define print_type(count,stmt) \\
do { \\
printf(\"[\"); \\
for (size_t i = 0; i < (count); ++i) { \\
stmt; \\
} \\
printf(\"]\\n\"); \\
} while (0)
struct cmplex {
int foo;
double bar;
};
int main() {
srand(time(NULL));
int intarr[] = { 1,-5,7,3,20,2 };
print_type(NELEMS(intarr),printf(\"%d,\",intarr[i]));
shuffle(intarr,NELEMS(intarr),sizeof(intarr[0]));
print_type(NELEMS(intarr),intarr[i]));
struct cmplex cmparr[] = {
{ 1,3.14 },{ 5,7.12 },{ 9,8.94 },{ 20,1.84 }
};
print_type(NELEMS(intarr),printf(\"{%d %f},cmparr[i].foo,cmparr[i].bar));
shuffle(cmparr,NELEMS(cmparr),sizeof(cmparr[0]));
print_type(NELEMS(intarr),cmparr[i].bar));
return 0;
}
void shuffle(int *array,size_t n) {
struct timeval tv;
gettimeofday(&tv,NULL);
int usec = tv.tv_usec;
srand48(usec);
if (n > 1) {
size_t i;
for (i = n - 1; i > 0; i--) {
size_t j = (unsigned int) (drand48()*(i+1));
int t = array[j];
array[j] = array[i];
array[i] = t;
}
}
}
void main ()
{
int elesize = sizeof (int);
int i;
int r;
int src [20];
int tgt [20];
for (i = 0; i < 20; src [i] = i++);
srand ( (unsigned int) time (0) );
for (i = 20; i > 0; i --)
{
r = rand () % i;
memcpy (&tgt [20 - i],&src [r],elesize);
memcpy (&src [r],&src [i - 1],elesize);
}
for (i = 0; i < 20; printf (\"%d \",tgt [i++] ) );
}
randn(int n)
swap(int a[],size_t i,size_t j)
swap(int a[],size_t j) {
int temp = a[i]; a[i] = a[j]; a[j] = temp;
}
a[i]
a[j]
void silly_shuffle(size_t n,int a[n]) {
for (size_t i = 0; i < n; i++)
swap(a,randn(n),randn(n)); // swap two random elements
}
void bad_shuffle(size_t n,i,randn(n));
}
void fisher_yates_shuffle(size_t n,i+randn(n-1-i)); // swap element with random later element
}
static inline void shuffle(size_t n,int arr[])
{
size_t rng;
size_t i;
int tmp[n];
int tmp2[n];
memcpy(tmp,arr,sizeof(int) * n);
bzero(tmp2,sizeof(int) * n);
srand(time(NULL));
i = 0;
while (i < n)
{
rng = rand() % (n - i);
while (tmp2[rng] == 1)
++rng;
tmp2[rng] = 1;
arr[i] = tmp[rng];
++i;
}
}
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