Add queue code

jbee37142 · jbee37142 · commit bb32865ccd76 · 2017-05-30T11:31:01.000+09:00
diff --git a/src/test/java/datastructure/queue/QueueWithTwoStack.java b/src/test/java/datastructure/queue/QueueWithTwoStack.java
@@ -0,0 +1,75 @@
+package datastructure.queue;
+
+import org.junit.Test;
+
+import java.util.Stack;
+
+import static org.hamcrest.CoreMatchers.is;
+import static org.junit.Assert.assertThat;
+
+public class QueueWithTwoStack {
+    @Test
+    public void test() {
+        MyQueue<Integer> queue = new MyQueue<>();
+        queue.offer(1);
+        queue.offer(2);
+        queue.offer(3);
+        queue.offer(4);
+
+        assertThat(queue.size(), is(4));
+
+        assertThat(queue.poll(), is(1));
+        assertThat(queue.poll(), is(2));
+        assertThat(queue.poll(), is(3));
+        assertThat(queue.poll(), is(4));
+
+        assertThat(queue.size(), is(0));
+    }
+
+    public class MyQueue<T> {
+        private Stack<T> stack1;
+        private Stack<T> stack2;
+
+        public MyQueue() {
+            stack1 = new Stack<T>();
+            stack2 = new Stack<T>();
+        }
+
+        public void offer(T elm) {
+//             1. 아예 stack2를 queue와 동일하게 데이터를 저장하는 방법
+//            while (!stack2.isEmpty()) {
+//                stack1.push(stack2.pop());
+//            }
+//            stack1.push(elm);
+//
+//            while (!stack1.isEmpty()) {
+//                stack2.push(stack1.pop());
+//            }
+
+            // 2. poll할 때만 queue처럼 반환하는 방법
+            stack1.push(elm);
+        }
+
+        public T poll() {
+//             1. 아예 stack2를 queue와 동일하게 데이터를 저장하는 방법
+//            return stack2.pop();
+
+//             2. poll할 때만 queue처럼 반환하는 방법
+            if (stack2.isEmpty()) {
+                while(!stack1.isEmpty()) {
+                    stack2.push(stack1.pop());
+                }
+            }
+            return stack2.pop();
+
+        }
+
+        public int size() {
+//             1. 아예 stack2를 queue와 동일하게 데이터를 저장하는 방법
+//            return stack2.size();
+
+//             2. poll할 때만 queue처럼 반환하는 방법
+            return stack1.size() + stack2.size();
+        }
+    }
+}
diff --git a/src/test/java/datastructure/queue/ReverseQueueTest.java b/src/test/java/datastructure/queue/ReverseQueueTest.java
@@ -0,0 +1,37 @@
+package datastructure.queue;
+
+import org.junit.Test;
+
+import java.util.LinkedList;
+import java.util.Queue;
+import java.util.Stack;
+
+import static org.hamcrest.CoreMatchers.is;
+import static org.junit.Assert.assertThat;
+
+public class ReverseQueueTest {
+    @Test
+    public void test() {
+        Queue<Integer> que = new LinkedList<>();
+        que.offer(1);
+        que.offer(2);
+        que.offer(3);
+
+        reverseQueue(que);
+
+        assertThat(que.poll(), is(3));
+        assertThat(que.poll(), is(2));
+        assertThat(que.poll(), is(1));
+    }
+
+    public Queue<Integer> reverseQueue(Queue<Integer> que) {
+        Stack<Integer> stack = new Stack<>();
+        while (!que.isEmpty()) {
+            stack.push(que.poll());
+        }
+        while(!stack.isEmpty()) {
+            que.offer(stack.pop());
+        }
+        return que;
+    }
+}
