输出1——n的排列（深度优先搜索）

样例输入：

3

样例输出：

123
132
213
231
312
321

#include <stdio.h>
int n;

void dfs(int step,int* a,int* book)
{
    int i;
    if(step == n)
    {
        for(i = 0;i < n;i++)
        {
            printf("%d",a[i]);
        }
        printf("
");
        return ; 
    }
    
    for(i = 0;i < n;i++)
    {
        if(book[i] == 0)
        {
            a[step] = i+1;
            book[i] = 1;
            dfs(step+1,a,book);
            book[i] = 0;
        }
    }
}
int main()
{
    scanf("%d",&n);
    int a[n+1],book[n+1],i;
    for(i = 0;i < n;i++)
    {
        a[i] = 0;
        book[i] = 0;
    }
    dfs(0,a,book);
    return 0;
}