import java.util.Stack;
import java.util.Scanner;
public class Calc {
public static void main (String [] args){
String expression;
Scanner input = new Scanner(System.in);
System.out.println("Введите выражение: ");
expression = input.nextLine();
String regex="\\d{3}";
System.out.println("Результат расчета: "+new Calc().decide(expression));
}
public double decide (String expression) {
String prepared = preparingExpression(expression);
String rpn = ExpressionToRPN(prepared);
return RPNtoAnswer(rpn);
}
private String preparingExpression (String expression){
String preperedExpression = new String();
for(int token = 0; token < expression.length(); token++){
char symbol = expression.charAt(token);
if(symbol == '-'){
if(token == 0) preperedExpression +='0';
else if(expression.charAt(token-1) == '(') preperedExpression +='0';
}
preperedExpression+=symbol;
}
return preperedExpression;
}
public static String ExpressionToRPN(String Expr){
String current = "";
Stack<Character> stack = new Stack<>();
int priority;
for(int i = 0; i <Expr.length();i++){
priority = getPriority(Expr.charAt(i));
if(priority == 0)current+=Expr.charAt(i);
if(priority == 1)stack.push(Expr.charAt(i));
if(priority > 1){
current+=' ';
while(!stack.empty()){
if(getPriority(stack.peek()) >=priority)current+=stack.pop();
else break;
}
stack.push(Expr.charAt(i));
}
if (priority == -1){
current+=' ';
while(getPriority(stack.peek()) !=1)current+=stack.pop();
stack.pop();
}
}
while(!stack.empty())current+=stack.pop();
return current;
}
public static double RPNtoAnswer(String rpn){
String operand = new String();
Stack<Double> stack = new Stack<>();
for(int i=0; i < rpn.length();i++){
if(rpn.charAt(i) == ' ')continue;
if(getPriority(rpn.charAt(i)) == 0){
while( rpn.charAt(i) != ' ' && getPriority(rpn.charAt(i)) == 0){
operand+=rpn.charAt(i++);
if(i == rpn.length())break;}
stack.push(Double.parseDouble(operand));
operand = new String();
}
if(getPriority(rpn.charAt(i)) >1 ){
double a = stack.pop(), b = stack.pop();
if(rpn.charAt(i) == '+')stack.push(b+a);
if(rpn.charAt(i) == '-')stack.push(b-a);
if(rpn.charAt(i) == '*')stack.push(b*a);
if(rpn.charAt(i) == '/')stack.push(b/a);
}
}
return stack.pop();
}
private static int getPriority(char token){
if(token == '*' || token == '/') return 3;
else if(token == '+' || token == '-') return 2;
else if(token == '(') return 1;
else if(token == ')') return -1;
else return 0;
}
}
