求1-9组成数字的全序列

#include<stdio.h>
int a[10],book[10],n;
void dfs(int step){
	int i;
	if(step==n+1){
		for(i=1;i<=n;i++)
		printf("%d",a[i]);
		printf("\n");
		return;
	}
	for(i=1;i<=n;i++){
		if(book[i]==0){
			a[step]=i;
			book[i]=1;
			dfs(step+1);
			book[i]=0;
		}
	}
	return;
}
int main(){
	scanf("%d",&n);
	dfs(1);
	return 0;	
}