RealExampleBasedQuestion/InfixPostfix.java at master · YPreety/RealExampleBasedQuestion · GitHub

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package Solutions;

import java.util.Stack;

interface Pattern {
	public String conversion(String exp);
}

public class InfixPostfix {

	public static void main(String[] args) {
		String infix = "a+b*c";

		InfixToPostfixPattern ip = new InfixToPostfixPattern();

		String postfix = ip.conversion(infix);
		System.out.println("Infix:   " + infix);
		System.out.println("Postfix: " + postfix);

	}

}

class InfixToPostfixPattern implements Pattern {

	@Override
	public String conversion(String exp) {

		int priority = 0;// for the priority of operators.

		String postfix = "";

		Stack<Character> s1 = new Stack<Character>();

		for (int i = 0; i < exp.length(); i++) {
			char ch = exp.charAt(i);
			if (ch == '+' || ch == '-' || ch == '*' || ch == '/' || ch == '%') {
				// check the precedence
				if (s1.size() <= 0)
					s1.push(ch);
				else {
					Character chTop = (Character) s1.peek();
					if (chTop == '*' || chTop == '/')
						priority = 1;
					else
						priority = 0;
					if (priority == 1) {
						if (ch == '*' || ch == '/' || ch == '%') {
							postfix += s1.pop();
							i--;
						} else { // Same
							postfix += s1.pop();
							i--;
						}
					} else {
						if (ch == '+' || ch == '-') {
							postfix += s1.pop();
							s1.push(ch);
						} else
							s1.push(ch);
					}
				}
			} else {
				postfix += ch;
			}
		}
		int len = s1.size();
		for (int j = 0; j < len; j++)
			postfix += s1.pop();
		return postfix;

	}

}