collections

whatsmars-common/src/test/java/org/hongxi/java/util/collections/ListReverseTest.java

+package org.hongxi.java.util.collections;
+
+/**
+ * @author shenhongxi 2019/8/12
+ */
+public class ListReverseTest {
+
+    public static void main(String[] args) {
+        SimpleList<Integer> list = new SimpleList<>();
+        list.add(1);
+        list.add(2);
+        list.add(3);
+        System.out.println(list);
+        list.reverse();
+        System.out.println(list);
+    }
+}

whatsmars-common/src/test/java/org/hongxi/java/util/collections/SimpleList.java

+package org.hongxi.java.util.collections;
+
+/**
+ * @author shenhongxi 2019/8/12
+ *
+ * @see java.util.LinkedList
+ */
+public class SimpleList<E> {
+
+    int size;
+    Node<E> first;
+    Node<E> last;
+
+    void add(E e) {
+        final Node<E> l = last;
+        final Node<E> newNode = new Node<>(e, null);
+        last = newNode;
+        if (l == null)
+            first = newNode;
+        else
+            l.next = newNode;
+        size++;
+    }
+
+    void reverse() {
+        if (first == null) return;
+        last = first;
+        Node<E> pre = first;
+        Node<E> curr = pre.next;
+        while (curr != null) {
+            pre.next = curr.next;
+            curr.next = first;
+            first = curr;
+            curr = pre.next;
+        }
+    }
+
+    static class Node<E> {
+        E item;
+        Node<E> next;
+
+        Node(E item, Node<E> next) {
+            this.item = item;
+            this.next = next;
+        }
+    }
+
+    @Override
+    public String toString() {
+        StringBuilder s = new StringBuilder();
+        for (Node<E> p = first; p != null; p = p.next) {
+            s.append(p.item);
+            if (p != last) {
+                s.append(", ");
+            }
+        }
+        return "[" + s.toString() + "]";
+    }
+}

whatsmars-common/src/test/java/org/hongxi/java/util/collections/SimpleStack.java

+package org.hongxi.java.util.collections;
+
+import java.util.ArrayList;
+import java.util.EmptyStackException;
+import java.util.List;
+
+/**
+ * @author shenhongxi 2019/8/12
+ *
+ * @see java.util.Stack
+ */
+public class SimpleStack<E> {
+
+    private int size;
+
+    private List<E> elements = new ArrayList<>();
+
+    public void push(E ele) {
+        if (elements.size() > size) {
+            elements.set(size, ele);
+        } else {
+            elements.add(ele);
+        }
+        size++;
+    }
+
+    public E pop() {
+        if (size == 0) {
+            throw new EmptyStackException();
+        }
+        return elements.set(--size, null);
+    }
+
+    public int size() {
+        return size;
+    }
+}

whatsmars-common/src/test/java/org/hongxi/java/util/collections/StackTest.java

+package org.hongxi.java.util.collections;
+
+/**
+ * @author shenhongxi 2019/8/12
+ */
+public class StackTest {
+
+    public static void main(String[] args) {
+        SimpleStack<Integer> stack = new SimpleStack<>();
+        stack.push(1);
+        stack.push(2);
+        stack.push(3);
+        System.out.println(stack.pop());
+        System.out.println(stack.pop());
+        System.out.println(stack.pop());
+    }
+}