I Can Guess the Data Structure! UVA11995

#include <iostream>#include <cstdio>#include <cstdlib>#include <cmath>#include <queue>#include <algorithm>#include <vector>#include <cstring>#include <stack>#include <cctype>#include <utility>   #include <map>#include <string>  #include <climits> #include <set>#include <string>    #include <sstream>#include <utility>   #include <ctime>using std::priority_queue;using std::vector;using std::swap;using std::stack;using std::sort;using std::max;using std::min;using std::pair;using std::map;using std::string;using std::cin;using std::cout;using std::set;using std::queue;using std::string;using std::istringstream;using std::make_pair;using std::greater;using std::endl;char print[3][20] = {"stack", "queue", "priority queue"};int main(){int n;while(~scanf("%d", &n)){stack<int> st;queue<int> que;priority_queue<int> pque;bool is[3] = {true, true, true};int op, num;for(int i = 0; i < n; ++i){scanf("%d%d", &op, &num);if(is[0]){if(op == 1){st.push(num);}else{if(st.empty() || st.top() != num)is[0] = false;elsest.pop();}}if(is[1]){if(op == 1){que.push(num);}else{if(que.empty() || que.front() != num)is[1] = false;elseque.pop();}}if(is[2]){if(op == 1){pque.push(num);}else{if(pque.empty() || pque.top() != num)is[2] = false;elsepque.pop();}}}int ans, count = 0;for(int i = 0; i < 3; ++i)if(is[i]){++count;ans = i;}switch(count){case 0:printf("impossible\n"); break;case 1:printf("%s\n", print[ans]); break;default:printf("not sure\n"); break;}}return 0;}