Java 火车出站序列

火车出站序列：
思路：
三个变量：待进站火车个数，待出站火车个数，已出站火车个数

import com.sun.xml.internal.bind.v2.schemagen.xmlschema.List;

import java.util.ArrayList;
import java.util.Scanner;
import java.util.Stack;
import java.util.TreeSet;
import java.util.Set;
public class Train {

public static boolean isLegal(int[] in,int[] out,int n){
int i=0;
int j=0;
Stack<Integer>  stack=new Stack<>();
while (i<n){
if(in[i]==out[j]){
i++;
j++;
}
else{
if(stack.empty()){
stack.push(in[i]);
i++;
}
else {
int top=stack.peek();
if(top==out[j]){
j++;
stack.pop();

}
else{
if(i<n){
stack.push(in[i]);
i++;
}
}
}
}
}

while(!stack.empty()&&j<n){
int top=stack.pop();
if(top==out[j]){
j++;
}
else {
return false;
}

}

return true;
}

public static void swap(int[] arr,int i,int j){
int tmp=arr[i];
arr[i]=arr[j];
arr[j]=tmp;
}

public static  void  Permutation(int []arr,int start,int N, ArrayList<int[]> result){
if(start==N){
return;
}
if(start==N-1){
int [] str=arr.clone();//数组拷贝
result.add(str);
return;
}
for(int i=start;i<N;i++){
swap(arr,i,start);
Permutation(arr,start+1,N,result);
swap(arr,i,start);
}
}

public static void main(String[] args) {
Scanner in=new Scanner(System.in);
while(in.hasNext()) {//有多组测试用例
int N = in.nextInt();//[1,9]
int[] arr = new int
;
for (int i = 0; i < N; i++) {
arr[i] = in.nextInt();
}

ArrayList<int[]> result = new ArrayList<>();//很多组，
int start = 0;
Permutation(arr, start, N, result);
Set<String> set = new TreeSet<String>();
for (int[] out : result) {//遍历result
if (isLegal(arr, out, N)) {
StringBuffer sb = new StringBuffer();
for (int i = 0; i < N - 1; i++) {
sb.append(out[i] + " ");

}

sb.append(out[N - 1]);
set.add(sb.toString());
}

for (String s : set) {//遍历 里是string的set
System.out.println(s);
}
}
}

}

}