UVA - 11995

There is a bag-like data structure, supporting two operations:
1 x Throw an element x into the bag. 2 Take out an element from the bag.
Given a sequence of operations with return values, you’re going to guess the data structure. It is a stack (Last-In, First-Out), a queue (First-In, First-Out), a priority-queue (Always take out larger elements first) or something else that you can hardly imagine!
Input There are several test cases. Each test case begins with a line containing a single integer n (1 ≤ n ≤ 1000). Each of the next n lines is either a type-1 command, or an integer 2 followed by an integer x. That means after executing a type-2 command, we get an element x without error. The value of x is always a positive integer not larger than 100. The input is terminated by end-of-file (EOF).
Output
For each test case, output one of the following:
stack It’s definitely a stack. queue It’s definitely a queue. priority queue It’s definitely a priority queue. impossible It can’t be a stack, a queue or a priority queue. not sure It can be more than one of the three data structures mentioned above.

题目大意：有一个袋状的数据结构，支持两个操作：1 x将一个元素x放入包中，2从包里取出一个元素。现给出一系列操作，问该操作过程符合哪种或哪几种数据结构。

思路：模拟stack、queue、priority_queue，判断是否符合这些结构。

代码如下：

#include
#include
#include
using namespace std;

const int maxn=1005;
int a[maxn],b[maxn];

bool issta(int n)
{
	int i;
	stack s;
	for (i=0;i q;
	for (i=0;i pq;
	for (i=0;i