39 lines
1.0 KiB
Java
39 lines
1.0 KiB
Java
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import java.util.*;
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public class Postfix {
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public static void main(String[] args) {
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Scanner scanner = new Scanner(System.in);
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String post = scanner.nextLine(); // Takes input with spaces in between eg. "1 21 +"
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System.out.println(postfixEvaluate(post));
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}
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// Evaluates the given postfix expression string and returns the result.
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public static int postfixEvaluate(String exp) {
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Stack<Integer> s = new Stack<Integer> ();
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Scanner tokens = new Scanner(exp);
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while (tokens.hasNext()) {
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if (tokens.hasNextInt()) {
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s.push(tokens.nextInt()); // If int then push to stack
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} else { // else pop top two values and perform the operation
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int num2 = s.pop();
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int num1 = s.pop();
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String op = tokens.next();
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if (op.equals("+")) {
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s.push(num1 + num2);
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} else if (op.equals("-")) {
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s.push(num1 - num2);
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} else if (op.equals("*")) {
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s.push(num1 * num2);
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} else {
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s.push(num1 / num2);
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}
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// "+", "-", "*", "/"
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}
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}
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return s.pop();
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}
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}
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