A479.最小栈

用空间换时间——维护栈中最小值

#include <iostream>
#include <string>
#include <stack>
using namespace std;

class int_stack {
    //stk:维护栈里元素
    //minv:维护进栈后最小元素
    stack<int> stk, minv;
    public:
        void push(int x) {
            stk.push(x);
            if (minv.empty()) minv.push(x);
            else minv.push(min(minv.top(), x));
        }
        void pop(void) {
            if (stk.empty()) {
                cout << "error\n";
                return;
            }
            stk.pop();
            minv.pop();
        }
        void top(void) {
            if (stk.empty()) {
                cout << "error\n";
                return;
            }
            cout << stk.top() << '\n';
        }
        void getmin(void) {
            if (minv.empty()) {
                cout << "error\n";
                return;
            }
            cout << minv.top() << '\n';
        }
} stk;
int n;
string op; int x;

int main() {
    cin >> n;
    while (n--) {
        cin >> op;
        if (op == "push") {
            cin >> x;
            stk.push(x);
        }
        if (op == "pop") {
            stk.pop();
        }
        if (op == "top") {
            stk.top();
        }
        if (op == "get_min") {
            stk.getmin();
        }
     }
    return 0;
}