新增章节：[双单向链表]

book.toml

@@ -1,7 +1,7 @@
 [book]
 authors = ["sunface"]
 language = "zh-CN"
-title = "Rust语言圣经(Rust教程 Rust Course)"
+title = "Rust语言圣经(Rust Course)"
 src = "src"
 
 [output.html]

src/too-many-lists/advanced-lists/double-singly.md

@@ -20,3 +20,201 @@ struct List<T> {
 }
 ```
 
+这里将之前的 `List` 引入进来，并重命名为 `Stack`，接着，创建一个新的链表。现在既可以向左增长又可以向右增长。
+
+```rust
+pub struct Stack<T> {
+    head: Link<T>,
+}
+
+type Link<T> = Option<Box<Node<T>>>;
+
+struct Node<T> {
+    elem: T,
+    next: Link<T>,
+}
+
+impl<T> Stack<T> {
+    pub fn new() -> Self {
+        Stack { head: None }
+    }
+
+    pub fn push(&mut self, elem: T) {
+        let new_node = Box::new(Node {
+            elem: elem,
+            next: self.head.take(),
+        });
+
+        self.head = Some(new_node);
+    }
+
+    pub fn pop(&mut self) -> Option<T> {
+        self.head.take().map(|node| {
+            let node = *node;
+            self.head = node.next;
+            node.elem
+        })
+    }
+
+    pub fn peek(&self) -> Option<&T> {
+        self.head.as_ref().map(|node| {
+            &node.elem
+        })
+    }
+
+    pub fn peek_mut(&mut self) -> Option<&mut T> {
+        self.head.as_mut().map(|node| {
+            &mut node.elem
+        })
+    }
+}
+
+impl<T> Drop for Stack<T> {
+    fn drop(&mut self) {
+        let mut cur_link = self.head.take();
+        while let Some(mut boxed_node) = cur_link {
+            cur_link = boxed_node.next.take();
+        }
+    }
+}
+```
+
+稍微修改下 `push` 和 `pop`：
+```rust
+pub fn push(&mut self, elem: T) {
+    let new_node = Box::new(Node {
+        elem: elem,
+        next: None,
+    });
+
+    self.push_node(new_node);
+}
+
+fn push_node(&mut self, mut node: Box<Node<T>>) {
+    node.next = self.head.take();
+    self.head = Some(node);
+}
+
+pub fn pop(&mut self) -> Option<T> {
+    self.pop_node().map(|node| {
+        node.elem
+    })
+}
+
+fn pop_node(&mut self) -> Option<Box<Node<T>>> {
+    self.head.take().map(|mut node| {
+        self.head = node.next.take();
+        node
+    })
+}
+```
+
+现在可以开始构造新的链表:
+```rust
+pub struct List<T> {
+    left: Stack<T>,
+    right: Stack<T>,
+}
+
+impl<T> List<T> {
+    fn new() -> Self {
+        List { left: Stack::new(), right: Stack::new() }
+    }
+}
+```
+
+当然，还有一大堆左左右右类型的操作:
+```rust
+pub fn push_left(&mut self, elem: T) { self.left.push(elem) }
+pub fn push_right(&mut self, elem: T) { self.right.push(elem) }
+pub fn pop_left(&mut self) -> Option<T> { self.left.pop() }
+pub fn pop_right(&mut self) -> Option<T> { self.right.pop() }
+pub fn peek_left(&self) -> Option<&T> { self.left.peek() }
+pub fn peek_right(&self) -> Option<&T> { self.right.peek() }
+pub fn peek_left_mut(&mut self) -> Option<&mut T> { self.left.peek_mut() }
+pub fn peek_right_mut(&mut self) -> Option<&mut T> { self.right.peek_mut() }
+```
+
+其中最有趣的是：还可以来回闲逛了。
+```rust
+pub fn go_left(&mut self) -> bool {
+    self.left.pop_node().map(|node| {
+        self.right.push_node(node);
+    }).is_some()
+}
+
+pub fn go_right(&mut self) -> bool {
+    self.right.pop_node().map(|node| {
+        self.left.push_node(node);
+    }).is_some()
+}
+```
+
+这里返回 `bool` 是为了告诉调用者我们是否成功的移动。最后，再来测试下：
+```rust
+#[cfg(test)]
+mod test {
+    use super::List;
+
+    #[test]
+    fn walk_aboot() {
+        let mut list = List::new();             // [_]
+
+        list.push_left(0);                      // [0,_]
+        list.push_right(1);                     // [0, _, 1]
+        assert_eq!(list.peek_left(), Some(&0));
+        assert_eq!(list.peek_right(), Some(&1));
+
+        list.push_left(2);                      // [0, 2, _, 1]
+        list.push_left(3);                      // [0, 2, 3, _, 1]
+        list.push_right(4);                     // [0, 2, 3, _, 4, 1]
+
+        while list.go_left() {}                 // [_, 0, 2, 3, 4, 1]
+
+        assert_eq!(list.pop_left(), None);
+        assert_eq!(list.pop_right(), Some(0));  // [_, 2, 3, 4, 1]
+        assert_eq!(list.pop_right(), Some(2));  // [_, 3, 4, 1]
+
+        list.push_left(5);                      // [5, _, 3, 4, 1]
+        assert_eq!(list.pop_right(), Some(3));  // [5, _, 4, 1]
+        assert_eq!(list.pop_left(), Some(5));   // [_, 4, 1]
+        assert_eq!(list.pop_right(), Some(4));  // [_, 1]
+        assert_eq!(list.pop_right(), Some(1));  // [_]
+
+        assert_eq!(list.pop_right(), None);
+        assert_eq!(list.pop_left(), None);
+
+    }
+}
+```
+
+```shell
+> cargo test
+
+     Running target/debug/lists-5c71138492ad4b4a
+
+running 16 tests
+test fifth::test::into_iter ... ok
+test fifth::test::basics ... ok
+test fifth::test::iter ... ok
+test fifth::test::iter_mut ... ok
+test fourth::test::into_iter ... ok
+test fourth::test::basics ... ok
+test fourth::test::peek ... ok
+test first::test::basics ... ok
+test second::test::into_iter ... ok
+test second::test::basics ... ok
+test second::test::iter ... ok
+test second::test::iter_mut ... ok
+test third::test::basics ... ok
+test third::test::iter ... ok
+test second::test::peek ... ok
+test silly1::test::walk_aboot ... ok
+
+test result: ok. 16 passed; 0 failed; 0 ignored; 0 measured
+```
+
+上上下下，左左右右，BABA，哦耶，这个链表无敌了！
+
+以上是一个非常典型的<ruby>手指型数据结构<rt>finger data structure</rt></ruby>，在其中维护一个手指，然后操作所需的时间与手指的距离成正比。
+

内容变更记录.md

@@ -1,6 +1,11 @@
 # ChangeLog
 记录一些值得注意的变更。
 
+## 2022-03-28
+
+- 新增章节：[双单向链表](https://course.rs/too-many-lists/advanced-lists/double-singly.html)
+- 优化样式：增加目录中的区域性标题、修改 github 图标和说明，通过 js 增加访问者统计
+
 ## 2022-03-27
 
 - 新增章节: [不错的unsafe队列 - 额外的操作](https://course.rs/too-many-lists/unsafe-queue/extra-junk.html)