From 4e6040f247d09aaa2bed1bb2eb19f3700193d6d3 Mon Sep 17 00:00:00 2001
From: Stjepan Glavina <stjepang@gmail.com>
Date: Fri, 28 Oct 2016 02:31:23 +0200
Subject: [PATCH] Implement a simple doubly linked list

---
 examples/linked_list.rs | 102 +++++++++++++++++++++++++++++++++++++++-
 examples/skip_list.rs   |   2 -
 2 files changed, 101 insertions(+), 3 deletions(-)
 delete mode 100644 examples/skip_list.rs

diff --git a/examples/linked_list.rs b/examples/linked_list.rs
index f79c691..36b1ee7 100644
--- a/examples/linked_list.rs
+++ b/examples/linked_list.rs
@@ -1,2 +1,102 @@
-fn main() {
+extern crate vec_arena;
+
+use vec_arena::VecArena;
+
+struct Node<T> {
+    prev: usize,
+    next: usize,
+    value: T,
+}
+
+struct List<T> {
+    arena: VecArena<Node<T>>,
+    head: usize,
+    tail: usize,
+}
+
+impl<T> List<T> {
+    fn new() -> Self {
+        List {
+            arena: VecArena::new(),
+            head: !0,
+            tail: !0,
+        }
+    }
+
+    fn len(&self) -> usize {
+        self.arena.len()
+    }
+
+    fn new_node(&mut self, value: T) -> usize {
+        self.arena.insert(Node {
+            prev: !0,
+            next: !0,
+            value: value,
+        })
+    }
+
+    fn link(&mut self, a: usize, b: usize) {
+        if a != !0 { self.arena[a].next = b; }
+        if b != !0 { self.arena[b].prev = a; }
+    }
+
+    fn push_back(&mut self, value: T) -> usize {
+        let node = self.new_node(value);
+
+        let tail = self.tail;
+        self.link(tail, node);
+
+        self.tail = node;
+        if self.head == !0 {
+            self.head = node;
+        }
+        node
+    }
+
+    fn pop_front(&mut self) -> T {
+        let node = self.arena.remove(self.head);
+
+        self.link(!0, node.next);
+        self.head = node.next;
+        if node.next == !0 {
+            self.tail = !0;
+        }
+        node.value
+    }
+
+    fn remove(&mut self, index: usize) -> T {
+        let node = self.arena.remove(index);
+
+        self.link(node.prev, node.next);
+        if self.head == index { self.head = node.next; }
+        if self.tail == index { self.tail = node.prev; }
+
+        node.value
+    }
+}
+
+fn main() {
+    let mut list = List::new();
+
+    let one = list.push_back(1);
+    list.push_back(2);
+    list.push_back(3);
+
+    list.push_back(10);
+    let twenty = list.push_back(20);
+    list.push_back(30);
+
+    assert!(list.len() == 6);
+
+    assert!(list.remove(one) == 1);
+    assert!(list.remove(twenty) == 20);
+
+    assert!(list.len() == 4);
+
+    assert!(list.pop_front() == 2);
+    assert!(list.pop_front() == 3);
+    assert!(list.pop_front() == 10);
+    assert!(list.pop_front() == 30);
+
+    assert!(list.len() == 0);
 }
diff --git a/examples/skip_list.rs b/examples/skip_list.rs
deleted file mode 100644
index f79c691..0000000
--- a/examples/skip_list.rs
+++ /dev/null
@@ -1,2 +0,0 @@
-fn main() {
-}