From 07d33735c61971b65aacccb8bc90b0b9e47fada7 Mon Sep 17 00:00:00 2001
From: Timothy Warren <twarren@nabancard.com>
Date: Wed, 13 Mar 2019 12:34:22 -0400
Subject: [PATCH] Add Double Singly-Linked list example

---
 src/lib.rs    |   2 +
 src/silly1.rs | 140 ++++++++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 142 insertions(+)
 create mode 100644 src/silly1.rs

diff --git a/src/lib.rs b/src/lib.rs
index 4d2d0c6..73df62e 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -3,3 +3,5 @@ pub mod second;
 pub mod third;
 pub mod fourth;
 pub mod fifth;
+
+pub mod silly1;
diff --git a/src/silly1.rs b/src/silly1.rs
new file mode 100644
index 0000000..d94d6b2
--- /dev/null
+++ b/src/silly1.rs
@@ -0,0 +1,140 @@
+//! # The Double Singly-Linked List
+
+#[derive(Debug)]
+pub struct List<T> {
+    left: Stack<T>,
+    right: Stack<T>,
+}
+
+#[derive(Debug)]
+pub struct Stack<T> {
+    head: Link<T>,
+}
+
+type Link<T> = Option<Box<Node<T>>>;
+
+#[derive(Debug)]
+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,
+            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) -> Link<T> {
+        self.head.take().map(|mut node| {
+            self.head = node.next.take();
+            node
+        })
+    }
+
+    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();
+        }
+    }
+}
+
+
+impl<T> List<T> {
+    pub fn new() -> Self {
+        List{
+            left: Stack::new(),
+            right: Stack::new(),
+        }
+    }
+
+    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() }
+
+    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()
+    }
+}
+
+#[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.peek_right(), Some(&0));
+        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);
+    }
+}