From d463251ff1d28e7e47892b9f17c7c458e05d99c7 Mon Sep 17 00:00:00 2001
From: Gleb Koval <gleb@koval.net>
Date: Tue, 5 Nov 2024 19:05:33 +0000
Subject: [PATCH] Fix reverse polish stack argument order and add non-symmetric
 evaluation tests

Co-Authored-By: td1223
---
 src/main/java/ic/doc/ReversePolishStack.java     |  4 ++--
 src/test/java/ic/doc/IntOperatorTest.java        |  6 ++++++
 src/test/java/ic/doc/ReversePolishStackTest.java | 16 ++++++++++++++--
 3 files changed, 22 insertions(+), 4 deletions(-)

diff --git a/src/main/java/ic/doc/ReversePolishStack.java b/src/main/java/ic/doc/ReversePolishStack.java
index 0a2f164..5f8f75e 100644
--- a/src/main/java/ic/doc/ReversePolishStack.java
+++ b/src/main/java/ic/doc/ReversePolishStack.java
@@ -26,12 +26,12 @@ public class ReversePolishStack {
     }
 
     IntOperator intOperator = stack.pop();
-    Stack<Integer> args = new Stack<>();
+    List<Integer> args = new LinkedList<>();
     while (args.size() < intOperator.getOperands()) {
       if (stack.isEmpty()) {
         throw new ArithmeticException("Not enough arguments to evaluate operator");
       }
-      args.push(evaluateNext());
+      args.addFirst(evaluateNext());
     }
     return intOperator.evaluate(args);
   }
diff --git a/src/test/java/ic/doc/IntOperatorTest.java b/src/test/java/ic/doc/IntOperatorTest.java
index 027bdb6..691be9b 100644
--- a/src/test/java/ic/doc/IntOperatorTest.java
+++ b/src/test/java/ic/doc/IntOperatorTest.java
@@ -15,6 +15,12 @@ public class IntOperatorTest {
     assertThat(intOperator.evaluate(List.of(1, 2)), is(3));
   }
 
+  @Test
+  public void intOperatorCanEvaluateNonSymmetric() {
+    IntOperator intOperator = new IntOperator("-", 2, args -> args.get(0) - args.get(1));
+    assertThat(intOperator.evaluate(List.of(1, 2)), is(-1));
+  }
+
   @Test
   public void intOperatorThrowsOnInvalidArguments() {
     IntOperator intOperator = new IntOperator("+", 2, args -> args.get(0) + args.get(1));
diff --git a/src/test/java/ic/doc/ReversePolishStackTest.java b/src/test/java/ic/doc/ReversePolishStackTest.java
index ec4419f..c54d5be 100644
--- a/src/test/java/ic/doc/ReversePolishStackTest.java
+++ b/src/test/java/ic/doc/ReversePolishStackTest.java
@@ -30,6 +30,18 @@ public class ReversePolishStackTest {
     assertThat(reversePolishStack.evaluate(), is(35));
   }
 
+  @Test
+  public void canEvaluateReversePolishStackNonSymmetric() {
+    reversePolishStack.push(new IntOperator("10", 0, args -> 10));
+    reversePolishStack.push(new IntOperator("25", 0, args -> 25));
+    reversePolishStack.push(new IntOperator("+", 2, args -> args.get(0) + args.get(1)));
+    reversePolishStack.push(new IntOperator("9", 0, args -> 9));
+    reversePolishStack.push(new IntOperator("1", 0, args -> 1));
+    reversePolishStack.push(new IntOperator("-", 2, args -> args.get(0) - args.get(1)));
+    reversePolishStack.push(new IntOperator("*", 2, args -> args.get(0) * args.get(1)));
+    assertThat(reversePolishStack.evaluate(), is(280));
+  }
+
   @Test
   public void evaluatePushesBack() {
     reversePolishStack.push(new IntOperator("10", 0, args -> 10));
@@ -57,8 +69,8 @@ public class ReversePolishStackTest {
     reversePolishStack.push(new IntOperator("10", 0, args -> 10));
     reversePolishStack.push(new IntOperator("25", 0, args -> 25));
     reversePolishStack.push(new IntOperator("+", 2, args -> args.get(0) + args.get(1)));
-    reversePolishStack.push(new IntOperator("1", 0, args -> 10));
-    reversePolishStack.push(new IntOperator("9", 0, args -> 25));
+    reversePolishStack.push(new IntOperator("1", 0, args -> 1));
+    reversePolishStack.push(new IntOperator("9", 0, args -> 9));
     reversePolishStack.push(new IntOperator("-", 2, args -> args.get(0) - args.get(1)));
     reversePolishStack.push(new IntOperator("*", 2, args -> args.get(0) * args.get(1)));
     assertThat(reversePolishStack.toString(), is("10 25 + 1 9 - *"));