Java-Programs/postfix.java at main · VirajPatidar/Java-Programs · GitHub

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import java.util.*;

class postfix {

static int precedence(char ch)

{

switch (ch)

{

case '+':

case '-':

return 1;

case '*':

case '/':

return 2;

case '^':

return 3;

}

return -1;

}

static String infixToPostfix(String exp){

String result = new String("");

Stack<Character> stack = new Stack<>();

for (int i = 0; i<exp.length(); ++i){

char c = exp.charAt(i);

if (Character.isLetterOrDigit(c))

result += c;

else if (c == '(')

stack.push(c);

else if (c == ')'){

while (!stack.isEmpty() && stack.peek() != '(')

result += stack.pop();

if (!stack.isEmpty() && stack.peek() != '(')

return "Invalid Expression"; // invalid expression

else

stack.pop();

}

else{

while (!stack.isEmpty() && precedence(c) <= precedence(stack.peek())){

if(stack.peek() == '(')

return "Invalid Expression";

result += stack.pop();

}

stack.push(c);

}

while (!stack.isEmpty()){

if(stack.peek() == '(')

return "Invalid Expression";

result += stack.pop();

}

return result;

}

public static void main(String[] args){

Scanner sc = new Scanner((System.in));

System.out.println("Enter the infix expression to get its postfix form");

String exp = sc.nextLine();

System.out.println(infixToPostfix(exp));

sc.close();

}

Java-Programs/postfix.java at main · VirajPatidar/Java-Programs · GitHub

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