UVa 11995 I Can Guess the Data Structure

想法：

    既然C++提供STL了，那就直接拿來用，模擬實際情況，但取値或pop()的時候要注意該Container是否為empty，否則會Runtime Error。

	#include <cstdio>
	#include <stack>
	#include <queue>
	using namespace std;
	int main()
	{
	// freopen("input.txt","rt",stdin);
	int N, Command, num;
	while (scanf("%d", &N) != EOF) {
	stack<int> S;
	queue<int> Q;
	priority_queue<int> PQ;
	bool isStack = 1, isQueue = 1, isPriQueue = 1;
	while (N--) {
	scanf("%d%d", &Command, &num);
	if (Command == 1) {
	S.push(num);
	Q.push(num);
	PQ.push(num);
	}
	else {
	if (S.empty() || S.top() != num) isStack = 0;
	if (Q.empty() || Q.front() != num) isQueue = 0;
	if (PQ.empty() || PQ.top() != num) isPriQueue = 0;
	if (!S.empty()) S.pop();
	if (!Q.empty()) Q.pop();
	if (!PQ.empty()) PQ.pop();
	}
	}
	if (isStack + isQueue + isPriQueue > 1)
	puts("not sure");
	else if (isStack) puts("stack");
	else if (isQueue) puts("queue");
	else if (isPriQueue) puts("priority queue");
	else puts("impossible");
	}
	return 0;
	}

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