Write a java method that provides a String argument. The method needs to determi

Question

Write a java method that provides a String argument. The method needs to determine whether the parentheses, brackets, and curly braces are within the string, return true if they are balanced, false otherwise.

Write a java method that takes a postfix expression as a String argument. The expression can include positive or negative integers and operations ( + , – , * ) separated with white spaces. The method should return the result after evaluating the expression. You only need to implement the following operations: addition, subtraction, and multiplication.

Explanation / Answer

1)

import java.util.*;
public class SpecialCharacter {
   public static boolean isBracketMatch(String str) {

Stack<Character> stack = new Stack<Character>();
char first_char;
for(int i=0; i < str.length(); i++) {
first_char = str.charAt(i);

if(first_char == '(')
stack.push(first_char);
else if(first_char == '{')
stack.push(first_char);
else if(first_char == '[')
stack.push(first_char);
else if(first_char == ')')
if(stack.empty())
return false;
else if(stack.peek() == '(')
stack.pop();
else
return false;
else if(first_char == '}')
if(stack.empty())
return false;
else if(stack.peek() == '{')
stack.pop();
else
return false;
else if(first_char == ']')
if(stack.empty())
return false;
else if(stack.peek() == '[')
stack.pop();
else
return false;
}
return stack.empty();
}
   public static void main(String[] args) {
       SpecialCharacter ob=new SpecialCharacter();
String s="[]";
boolean result=ob.isBracketMatch(s);
System.out.println("Result :"+result);

   }
}

2)

import java.util.*;

public class Postfix {
   public static void main(String[] args) {
   public static int evaluatePostfix(String exp) throws Exception {
      
       Stack<Integer> stack = new Stack<>();
       exp = insertSpaces(exp);

       String[] tokens = exp.split(" ");

       for (String token: tokens) {
           if (token.length() == 0)
               continue; // extract the next token
           else if (token.charAt(0) == '+' || token.charAt(0) == '-' || token.charAt(0) == '/' || token.charAt(0) == '*') {
                   operatorSequence(stack, token.charAt(0));
           }
           else if (Character.isDigit(token.charAt(0))){
               stack.push(Integer.parseInt(token));
           }
           else
               throw new Exception("Invalid Expression: ");
       }
       return stack.pop();
   }

   public static void operatorSequence(
       Stack<Integer> stack, char operator) {
       int op1 = stack.pop();
       int op2 = stack.pop();

       switch (operator) {
           case '+': stack.push(op2 + op1); break;
           case '-': stack.push(op2 - op1); break;
           case '/': stack.push(op2 / op1); break;
           case '*': stack.push(op2 * op1);
       }
   }

   public static String insertSpaces(String s) {
       String res = "";

       for (int i = 0; i < s.length(); i++) {
           if (s.charAt(i) == '+' || s.charAt(i) == '-' || s.charAt(i) == '/' || s.charAt(i) == '*')
               res += " " + s.charAt(i) + " ";
           else
               res += s.charAt(i);
       }
       return res;
   }
}

Related Questions

Navigate

• Browse (All)
• Browse W
• Subjects

Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.