Add stack code

jbee37142 · jbee37142 · commit 50eff569e95b · 2017-05-30T10:34:00.000+09:00
diff --git a/src/test/java/datastructure/stack/IsPalindromeTest.java b/src/test/java/datastructure/stack/IsPalindromeTest.java
@@ -17,18 +17,22 @@ public class IsPalindromeTest {
     @Test
     public void test() {
         assertThat(isPalindrome("abba"), is(true));
+        assertThat(isPalindrome("dabccbad"), is(true));
+        assertThat(isPalindrome("abcba"), is(true));
+        assertThat(isPalindrome("fabccdedccbaf"), is(true));
+        assertThat(isPalindrome("fabccdedccbf"), is(false));
     }
 
     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;
-                }
+        for (int i = 0; i < str.length() / 2; i++) {
+            stack.add(charArr[i]);
+        }
+
+        for (int i = (str.length() + 1)/2; i < str.length(); i++) {
+            if (stack.pop() != charArr[i]) {
+                return false;
             }
         }
         return true;
diff --git a/src/test/java/datastructure/stack/MinimumStackTest.java b/src/test/java/datastructure/stack/MinimumStackTest.java
@@ -0,0 +1,61 @@
+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 MinimumStackTest {
+
+    /*
+        TASK
+        Stack에 저장된 값들 중 최소값을 반환하는 minStack() 함수를 구현한다.
+     */
+
+    @Test
+    public void test() {
+        MyStack stack = new MyStack();
+        stack.push(3);
+        stack.push(5);
+        stack.push(4);
+        stack.push(2);
+        stack.push(6);
+
+        assertThat(stack.min(), is(2));
+    }
+
+    public class MyStack {
+        private Stack<Integer> stack;
+        private Stack<Integer> minStack;
+
+        public MyStack() {
+            stack = new Stack<>();
+            minStack = new Stack<>();
+        }
+
+        public void push(int newVal) {
+            if (minStack.isEmpty() || newVal <= minStack.peek()) {
+                minStack.push(newVal);
+            }
+            stack.push(newVal);
+        }
+
+        public int pop() {
+            int val = stack.pop();
+            if (!minStack.isEmpty() && val == minStack.peek()) {
+                minStack.pop();
+            }
+            return val;
+        }
+
+        public int min() {
+            if (minStack.isEmpty()) {
+                throw new RuntimeException("");
+            }
+            return minStack.peek();
+        }
+    }
+}
