ADV-188 算法提高 排列数

　　0 < n <= 10!

解题思路：使用dfs来解排列数的题

直接上代码：

public class Main {
static int a[] = new int[11];//存数
static int book[] = new int[11];//标记数组
static final int value = 10;
static int n = 0;
static int count = 0;//计数，与n比较
public static void main(String[] args) {
Scanner s = new Scanner(System.in);
n = s.nextInt();
dfs(0);
}


private static void dfs(int step) {
if (step == value) {    //排列0--9十个数，step从0加到9，当step==10说明排列完成
count++;
if (count == n) {
for (int i = 0; i < value; i++)
System.out.print(a[i]);
}
}
for (int i = 0; i < value; i++) {
if (book[i] == 0) {
a[step] = i;
book[i] = 1;
dfs(step + 1);
book[i] = 0;//标记完后要释放
}
}
}


}