025 通过链表学Rust之使用栈实现双端队列

介绍

视频地址：https://www.bilibili.com/video/av78062009/
相关源码：https://github.com/anonymousGiga/Rust-link-list

详细内容

本节我们使用栈来实现双端队列。

实现栈

栈的实现基本上和最开始的单链表的实现差不多，如下：

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 }
  }
  fn push_node(&mut self, mut node: Box<Node<T>>) {
    node.next = self.head.take();
    self.head = Some(node);
  }
  pub fn push(&mut self, elem: T) {
    let node = Box::new(Node {
      elem: elem,
      next: None,
    });
    self.push_node(node);
  }
  fn pop_node(&mut self) -> Option<Box<Node<T>>> {
    self.head.take().map(|mut node| {
      self.head = node.next.take();
      node
    })
  }
  pub fn pop(&mut self) -> Option<T> {
    self.pop_node().map(|node| {
      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 link = self.head.take();
    while let Some(mut node) = link {
      link = node.next.take();
    }
  }
}

实现双端队列

代码如下：

pub struct List<T> {
  left: Stack<T>,
  right: Stack<T>,
}

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()
  }
}

测试及完整代码

如下：

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 }
    }
    fn push_node(&mut self, mut node: Box<Node<T>>) {
        node.next = self.head.take();
        self.head = Some(node);
    }
    pub fn push(&mut self, elem: T) {
        let node = Box::new(Node {
            elem: elem,
            next: None,
        });
        self.push_node(node);
    }
    fn pop_node(&mut self) -> Option<Box<Node<T>>> {
        self.head.take().map(|mut node| {
            self.head = node.next.take();
            node
        })
    }
    pub fn pop(&mut self) -> Option<T> {
        self.pop_node().map(|node| {
            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 link = self.head.take();
        while let Some(mut node) = link {
            link = node.next.take();
        }
    }
}

pub struct List<T> {
    left: Stack<T>,
    right: Stack<T>,
}

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.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);
    }
}