地址：http://acm.hdu.edu.cn/showproblem.php?pid=1022
题目：
Problem Description
As the new term comes, the Ignatius Train Station is very busy nowadays. A lot of student want to get back to school by train(because the trains in the Ignatius Train Station is the fastest all over the world ^v^). But here comes a problem, there is only one railway where all the trains stop. So all the trains come in from one side and get out from the other side. For this problem, if train A gets into the railway first, and then train B gets into the railway before train A leaves, train A can‘t leave until train B leaves. The pictures below figure out the problem. Now the problem for you is, there are at most 9 trains in the station, all the trains has an ID(numbered from 1 to n), the trains get into the railway in an order O1, your task is to determine whether the trains can get out in an order O2.
Input
The input contains several test cases. Each test case consists of an integer, the number of trains, and two strings, the order of the trains come in:O1, and the order of the trains leave:O2. The input is terminated by the end of file. More details in the Sample Input.
Output
The output contains a string "No." if you can‘t exchange O2 to O1, or you should output a line contains "Yes.", and then output your way in exchanging the order(you should output "in" for a train getting into the railway, and "out" for a train getting out of the railway). Print a line contains "FINISH" after each test case. More details in the Sample Output.
Sample Input
3 123 321
3 123 312
Sample Output
Yes.
in
in
in
out
out
out
FINISH
No.
FINISH
Hint
Hint
For the first Sample Input, we let train 1 get in, then train 2 and train 3.
So now train 3 is at the top of the railway, so train 3 can leave first, then train 2 and train 1.
In the second Sample input, we should let train 3 leave first, so we have to let train 1 get in, then train 2 and train 3.
Now we can let train 3 leave.
But after that we can‘t let train 1 leave before train 2, because train 2 is at the top of the railway at the moment.
So we output "No.".
思路：紫书上原题，题意是给你一个进站前的数列，判断这几个数能否通过类似入栈出栈的操作后得到题目所给的数列；
用栈来模拟就好。
ps：一定要注意输出格式！！！写完代码之后，愣是一直wa，开始是因为栈没清空，后又发现是输出格式不对！！！
血的教训，改了好半天！！！
1 #include <iostream>
2 #include <algorithm>
3 #include <cstdio>
4 #include <cmath>
5 #include <cstring>
6 #include <queue>
7 #include <stack>
8 #include <map>
9 #include <vector>
10 #include <string>
11
12 #define PI acos((double)-1)
13 #define E exp(double(1))
14 #define N 1000000
15 using namespace std;
16
17 int main (void)
18 {
19 int t,a,b,flag,c;
20 string s,e,code;
21 stack<int>sk;
22 while(scanf("%d",&t) == 1 && t)
23 {
24 cin>>s>>e;
25 flag=1;
26 a=b=c=0;
27 while(b<t)
28 {
29 if(s[a] == e[b])
30 {
31 a++;b++;
32 code[c++]=1;
33 code[c++]=0;
34 }
35 else if(!sk.empty() && e[b] == sk.top())
36 {
37 sk.pop();b++;
38 code[c++]=0;
39 }
40 else if(a < t)
41 {
42 sk.push(s[a++]);
43 code[c++]=1;
44 }
45 else
46 {
47 flag = 0;
48 break;
49 }
50 }
51 if(flag)
52 {
53 cout<<"Yes."<<endl;
54 for(int i = 0;i< 2*t;i++)
55 if(code[i])
56 cout<<"in"<<endl;
57 else
58 cout<<"out"<<endl;
59 }
60 else
61 cout<<"No."<<endl;
62 cout<<"FINISH"<<endl;
63 while(!sk.empty())
64 sk.pop();
65 }
66 return 0;
67 }