A postfix expression is of the form instead of the traditional infix expression which follows the form .
Your task is to write a program that takes advantage of the stack data structure and converts a given infix expression into its postfix expression.
INPUT
There will be only a single line of input, the string that denotes the infix expression to be converted into its postfix counterpart.
There are four arithmetic operations and capital letters used as variables/operands.
Look at the sample Input/Output for clarity
OUTPUT
Output the final postfix expression after converting it to postfix from infix.
Sample Input 0
A+B
Sample Output 0
AB+import java.util.Stack;
import java.util.*;
class Solution
{
static int Prec(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";
else
stack.pop();
}
else
{
while (!stack.isEmpty() && Prec(c) <= Prec(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);
String exp = sc.next();
System.out.println(infixToPostfix(exp));
}
}
