백준 1918번 후위 표기식 C++

출처 : https://www.acmicpc.net/problem/1918

 

#include <iostream>
#include <string>
#include <vector>
#include <math.h>
#include <algorithm>
#include <utility>
#include <stack>
#include <queue>
#include <math.h>
#include <set>
#include <map>
#include <list>
#include <unordered_map>
#include <unordered_set>
#include <iomanip>
#include <limits.h>

using namespace std;
using int64 = long long;

enum {
	OPERAND,
	OPERATOR
};

int GetType(char c) {
	if (c >= 'A' && c <= 'Z')
		return OPERAND;
	return OPERATOR;
}

int main() {
	ios_base::sync_with_stdio(false);
	cin.tie(NULL);
	cout.tie(NULL);

	string str;
	cin >> str;
	stack<char> st;
	for (int i = 0; i < str.length(); i++) {
		if (GetType(str[i]) == OPERAND) {
			cout << str[i];
			continue;
		}
		if (str[i] == '(') {
			st.push(str[i]);
			continue;
		}
		if (str[i] == ')') {
			while (st.top() != '(') {
				cout << st.top();
				st.pop();
			}
			st.pop();
			continue;
		}
		if (str[i] == '+' || str[i] == '-') {
			if (st.empty() || st.top() == '(') {
				st.push(str[i]);
				continue;
			}
			cout << st.top();
			st.pop();
			if (!st.empty() && (st.top() == '+' || st.top() == '-')) {
				cout << st.top();
				st.pop();
			}
			st.push(str[i]);
			continue;
		}
		if (str[i] == '*' || str[i] == '/') {
			if (st.empty() || st.top() == '(') {
				st.push(str[i]);
				continue;
			}
			if (st.top() == '*' || st.top() == '/') {
				cout << st.top();
				st.pop();
			}
			st.push(str[i]);
		}
	}
	while (!st.empty()) {
		cout << st.top();
		st.pop();
	}
};