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Moved StackPostfixNotation.java from the Others section to the Stack section (#4372)

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* Moved StackPostfixNotation.java from the Others section to the Stack section

* Put all stack related algo in a separate stack directory in the algorithms directory. The stack directory under data-structures now only contains various implementations of the stack data structure.

* formatted files
This commit is contained in:
Subhradeep Bera
2023-09-19 00:57:36 +05:30
committed by GitHub
parent a1844840fd
commit 26c2465328
13 changed files with 21 additions and 23 deletions
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65
src/main/java/com/thealgorithms/others/StackPostfixNotation.java
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@ -1,65 +0,0 @@
package com.thealgorithms.others;
import java.util.Scanner;
import java.util.Stack;
import java.util.function.BiFunction;
/**
* @brief Utility class evaluating postix expressions, cf. https://en.wikipedia.org/wiki/Reverse_Polish_notation
* @details The computation is done using Integers.
*/
public final class StackPostfixNotation {
private StackPostfixNotation() {
}
private static BiFunction<Integer, Integer, Integer> getOperator(final String operationSymbol) {
// note the order of operands
switch (operationSymbol) {
case "+":
return (a, b) -> b + a;
case "-":
return (a, b) -> b - a;
case "*":
return (a, b) -> b * a;
case "/":
return (a, b) -> b / a;
default:
throw new IllegalArgumentException("exp contains an unknown operation.");
}
}
private static void performOperation(Stack<Integer> s, final String operationSymbol) {
if (s.size() < 2) {
throw new IllegalArgumentException("exp is not a proper postfix expression (too few arguments).");
}
s.push(getOperator(operationSymbol).apply(s.pop(), s.pop()));
}
private static void consumeExpression(Stack<Integer> s, final String exp) {
Scanner tokens = new Scanner(exp);
while (tokens.hasNext()) {
if (tokens.hasNextInt()) {
s.push(tokens.nextInt());
} else {
performOperation(s, tokens.next());
}
}
tokens.close();
}
/**
* @brief Evaluates the given postfix expression.
* @param exp the expression to evaluate.
* @return the value of the given expression.
* @exception IllegalArgumentException exp is not a valid postix expression.
*/
public static int postfixEvaluate(final String exp) {
Stack<Integer> s = new Stack<Integer>();
consumeExpression(s, exp);
if (s.size() != 1) {
throw new IllegalArgumentException("exp is not a proper postfix expression.");
}
return s.pop();
}
}