题解 | 中缀表达式转后缀表达式

#include <iostream>
#include <string>
#include <vector>
#include <stack>


int main() {
    // deal with input
    std::string in, out;
    char c;
    while(std::cin >> c){
        in += c;
    }
    
    std::stack<char> stk;
    for(int i = 0; i < in.size(); ++i) {
        if(std::isalpha(in[i])) {
            out += in[i];
            continue;
        }
        if(in[i] == '(' || stk.empty()) {
            stk.push(in[i]);
            continue;
        }
        if(in[i] == ')') {
            while(stk.top() != '(') {
                out += stk.top();
                stk.pop();
            }
            out += stk.top();
            stk.pop();
            continue;
        }
        if(in[i] == '+' || in[i] == '-') {
            while(!stk.empty() && stk.top() != '(') {
                out += stk.top();
                stk.pop();
            }
            stk.push(in[i]);
        } else {
            while(!stk.empty() && stk.top() != '(' && (stk.top() == '*' || stk.top() == '/')) {
                out += stk.top();
                stk.pop();
            }
            stk.push(in[i]);
        }
    }
    while(!stk.empty()) {
        out += stk.top();
        stk.pop();
    }
    std::cout << out << std::endl;
    return 0;
}
// 64 位输出请用 printf("%lld")