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Postfix Notation using Stack #121

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Merged
varunu28 merged 2 commits into from
Oct 10, 2017
Merged

Postfix Notation using Stack #121

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Postfix Notation using Stack
manmeet-22 Oct 1, 2017
ae3342f
Added Extension
manmeet-22 Oct 3, 2017
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38 changes: 38 additions & 0 deletions Misc/StackPostfixNotation.java
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Original file line number Diff line number Diff line change
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import java.util.*;

public class Postfix {
public static void main(String[] args) {
Scanner scanner = new Scanner(System.in);
String post = scanner.nextLine(); // Takes input with spaces in between eg. "1 21 +"
System.out.println(postfixEvaluate(post));
}

// Evaluates the given postfix expression string and returns the result.
public static int postfixEvaluate(String exp) {
Stack<Integer> s = new Stack<Integer> ();
Scanner tokens = new Scanner(exp);

while (tokens.hasNext()) {
if (tokens.hasNextInt()) {
s.push(tokens.nextInt()); // If int then push to stack
} else { // else pop top two values and perform the operation
int num2 = s.pop();
int num1 = s.pop();
String op = tokens.next();

if (op.equals("+")) {
s.push(num1 + num2);
} else if (op.equals("-")) {
s.push(num1 - num2);
} else if (op.equals("*")) {
s.push(num1 * num2);
} else {
s.push(num1 / num2);
}

// "+", "-", "*", "/"
}
}
return s.pop();
}
}