题解 | #堆栈的使用#
堆栈的使用
https://www.nowcoder.com/practice/e91982a145944ceab6bb9a4a508e0e26
#include <bits/stdc++.h> using namespace std; stack<int> stk; int main(){ int n; while (cin >> n){ while (n --){ string op; cin >> op; if (op == "P"){ int x; cin >> x; stk.push(x); } else if (op == "O"){ if (!stk.empty()) stk.pop(); } else{ if (stk.empty()) puts("E"); else printf("%d\n", stk.top()); } } } return 0; }