Add stack code

Author: jbee37142

src/test/java/datastructure/stack/IsPalindromeTest.java

@@ -0,0 +1,36 @@
+package datastructure.stack;
+
+import org.junit.Test;
+
+import java.util.Stack;
+
+import static org.hamcrest.CoreMatchers.is;
+import static org.junit.Assert.assertThat;
+
+public class IsPalindromeTest {
+
+    /*
+        TASK
+        Stack 자료구조를 사용하여 회문을 판별한다.
+     */
+
+    @Test
+    public void test() {
+        assertThat(isPalindrome("abba"), is(true));
+    }
+
+    public boolean isPalindrome(String str) {
+        Stack<Character> stack = new Stack<>();
+        char[] charArr = str.toCharArray();
+        for (int i = 0; i < str.length(); i++) {
+            if (i <= str.length() / 2) {
+                stack.add(charArr[i]);
+            } else {
+                if (stack.pop() != charArr[i]) {
+                    return false;
+                }
+            }
+        }
+        return true;
+    }
+}

src/test/java/datastructure/stack/MyStackWithArrayListTest.java

@@ -0,0 +1,48 @@
+package datastructure.stack;
+
+import org.junit.Test;
+
+import java.util.ArrayList;
+import java.util.List;
+
+import static org.hamcrest.CoreMatchers.is;
+import static org.junit.Assert.assertThat;
+
+public class MyStackWithArrayListTest {
+    @Test
+    public void test() {
+        MyStackWithArrayList<Integer> stack = new MyStackWithArrayList<>();
+
+        stack.push(0);
+        stack.push(1);
+        stack.push(2);
+        stack.push(3);
+        stack.push(4);
+        stack.push(5);
+        stack.push(6);
+
+        assertThat(6, is(stack.pop()));
+        assertThat(5, is(stack.pop()));
+        assertThat(4, is(stack.pop()));
+        assertThat(3, is(stack.pop()));
+        assertThat(2, is(stack.pop()));
+        assertThat(1, is(stack.pop()));
+        assertThat(0, is(stack.pop()));
+    }
+
+    public class MyStackWithArrayList<T> {
+        private List<T> data;
+
+        public MyStackWithArrayList() {
+            data = new ArrayList<T>();
+        }
+
+        public void push(T i) {
+            data.add(i);
+        }
+
+        public T pop() {
+            return data.remove(data.size() - 1);
+        }
+    }
+}

src/test/java/datastructure/stack/MyStackWithArrayTest.java

@@ -0,0 +1,60 @@
+package datastructure.stack;
+
+import org.junit.Test;
+
+import static org.hamcrest.CoreMatchers.is;
+import static org.junit.Assert.assertThat;
+
+public class MyStackWithArrayTest {
+    @Test
+    public void test() {
+        MyStackWithArray stack = new MyStackWithArray();
+
+        stack.push(0);
+        stack.push(1);
+        stack.push(2);
+        stack.push(3);
+        stack.push(4);
+        stack.push(5);
+        stack.push(6);
+
+        assertThat(6, is(stack.pop()));
+        assertThat(5, is(stack.pop()));
+        assertThat(4, is(stack.pop()));
+        assertThat(3, is(stack.pop()));
+        assertThat(2, is(stack.pop()));
+        assertThat(1, is(stack.pop()));
+        assertThat(0, is(stack.pop()));
+
+//        java.lang.RuntimeException: Empty Stack!
+//        assertThat(0, is(stack.pop()));
+    }
+
+    public class MyStackWithArray {
+        private int[] data = new int[5];
+        private int topIndex = -1;
+
+        public synchronized void push(int i) {
+            topIndex++;
+            if (topIndex >= data.length) {
+                int[] oldData = data;
+                data = new int[data.length * 2];
+//                System.arraycopy(oldData, 0, data, 0, oldData.length);
+                for (int j = 0; j < oldData.length; j++) {
+                    data[j] = oldData[j];
+                }
+            }
+
+            data[topIndex] = i;
+        }
+
+        public synchronized int pop() {
+            if (topIndex < 0) {
+                throw new RuntimeException("Empty Stack!");
+            }
+//            int result = data[topIndex];
+//            topIndex--;
+            return data[topIndex--];
+        }
+    }
+}