7道经典栈、队列、堆的题目-简单计算器

class Solution {
public:
    void compute(std::stack<unsigned int> &number_stack,
                 std::stack<char> &operation_stack){
        if (number_stack.size() < 2){
            return;
        }
        unsigned int num2 = number_stack.top();
        number_stack.pop();
        unsigned int num1 = number_stack.top();
        number_stack.pop();
        if (operation_stack.top() == '+'){
            number_stack.push(num1 + num2);
        }
        else if(operation_stack.top() == '-'){
            number_stack.push(num1 - num2);
        }
        operation_stack.pop();
    }
    
    int calculate(string s) {
        enum state{STATE_BEGIN, NUMBER_STATE, OPERATION_STATE}STATE = STATE_BEGIN; 
        std::stack<unsigned int> number_stack;
        std::stack<char> operation_stack;
        unsigned int number = 0;
        bool compuate_flag = false;
        for (int i = 0; i < s.length(); i++){
            if (s[i] == ' '){
                continue;
            }
            switch(STATE){
            case STATE_BEGIN:
                if (s[i] >= '0' && s[i] <= '9'){
                    STATE = NUMBER_STATE;
                }
                else{
                    STATE = OPERATION_STATE;
                }
                i--;
                break;
            case NUMBER_STATE:
                if (s[i] >= '0' && s[i] <= '9'){
                    number = number * 10 + s[i] - '0';
                }
                else{
                    number_stack.push(number);
                    if (compuate_flag){
                        compute(number_stack, operation_stack);
                    }
                    number = 0;
                    i--;
                    STATE = OPERATION_STATE;
                }
                break;
            case OPERATION_STATE:
                if (s[i] == '+' || s[i] == '-'){
                    operation_stack.push(s[i]);
                    compuate_flag = true;
                }
                else if (s[i] == '('){
                    STATE = NUMBER_STATE;
                    compuate_flag = false;
                }
                else if (s[i] >= '0' && s[i] <= '9'){
                    STATE = NUMBER_STATE;                   
                    i--;
                }
                else if (s[i] == ')'){
                    compute(number_stack, operation_stack);
                }
                break;
            }
        }
        if (number != 0){
            number_stack.push(number);
            compute(number_stack, operation_stack);
        }
        if (number == 0 && number_stack.empty()){
            return 0;
        }
        return number_stack.top();
    }
};

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

class Solution {
private:
    stack<int> num;
    stack<char> op;
    int pri(char a){
        switch(a){
        case '+': return 1;
        case '-': return 1;
        case '*': return 2;
        case '/': return 2;
        case '(': return 3;
        default: return -1;
        }
    }
    void cal(){
        int b=num.top();num.pop();
        int a=num.top();num.pop();
        switch(op.top()){
        case '+':num.push(a+b);break;
        case '-':num.push(a-b);break;
        case '*':num.push(a*b);break;
        case '/':num.push(a/b);break;
        }
        op.pop();
    }
public:
    int calculate(string s) {
                string ss;
        for(int i=0;i<(int)s.size();i++){
            if(isdigit(s[i]))
                ss+=s[i];
            else if(s[i]==' ') continue;
            else{
                if(!ss.empty()){
                    num.push(stoi(ss));
                    ss.clear();
                }
                if(op.empty()||s[i]=='('||pri(op.top())<pri(s[i]) )
                    op.push(s[i]);
                else if(s[i]==')'){
                    while(op.top()!='(') cal();
                    op.pop();
                }
                else{
                    while(!op.empty()&&pri(op.top())<=pri(s[i])) cal();
                    op.push(s[i]);
                }
            }
        }
        if(!ss.empty()) num.push(stoi(ss));
        while(!op.empty()) cal();
        return num.top();
    }
};

int main(){
    Solution s;
    cout<<s.calculate("(1+(4+5+2)-3)+(6+8)")<<endl;
}