順列列挙でステップごとのメモリ確保無しでできると教わったのでやってみた

perm_recur.c

//$ gcc -std=m9 perm.c
#include<stdio.h>
#include<stdlib.h>
void swap_int(int *a,int *b){
	int t = *a;
 	*a = *b;
	*b = t;	
}
void print_int_array(int array[],int num){
	printf("[ ");
	for(int i=0;i<num;i++)printf("%d ",array[i]);
	printf("]\n");
}
void print_int_array_u(int array[],int num,void *user){
	print_int_array(array,num);
}
void perm_iter(int items[],int numItems,int depth,void (*callback)(int array[],int num,void *user),void *user){
	if(depth >= numItems){
		(*callback)(items,numItems,user);
		return;
	}
	for(int i=depth;i<numItems;i++){
		swap_int(&items[depth],&items[i]);
		perm_iter(items,numItems,depth+1,callback,user);
		swap_int(&items[depth],&items[i]);
	}
}

int main(int argc,char *argv[]){
	int *array = NULL;
	if(argc<=1){
		printf("usage : %s a[0] a[1] a[2] ...\n",argv[0]);
		exit(1);
	}
	array = malloc(sizeof(int)*(argc-1));
	for(int i=1;i<argc;i++){
		array[i-1] = atoi(argv[i]);
	}
	perm_iter(array,argc-1,0,&print_int_array_u,NULL);
	free(array);
	array=NULL;
	return 0;
}