珀尔 |实现堆栈

Perl 中的堆栈是遵循LIFO （后进先出）或FILO （先进后出）顺序的线性数据结构。
简单来说，堆栈是一个数组，其中插入和删除仅发生在称为堆栈顶部的一端。
推送是将元素插入堆栈的过程。
弹出是删除堆栈最顶层元素的过程。

制作堆栈

在 Perl 中创建堆栈相当简单。我们需要做的就是声明一个数组。
堆栈可能为空，如下所示：

@stack;

或者它可以被初始化：

@stack = (1, 2, 3);

将项目推入堆栈

可以使用push()函数或splice()函数来完成推送。

• 使用push() 推送：

  Syntax: push(@stack, list);
  Parameters:

  • @stack – The stack on which push is to be performed.
  • list – The elements to be pushed into a stack. These elements might be scalar, array, hash or any combination of these.

  例子：

  #!/usr/bin/perl
    
  # Intitialising the Stack
  @stack = (1..3);
    
  # Original stack
  print "Original Stack: @stack";
    
  # Scalar to be pushed
  $scalar = "scalar";
    
  # Array to be pushed
  @array = ("a", "r", "r", "a", "y");
    
  # Hash to be pushed
  %hash = ("Geeks" => 10, 
           "for Geeks" => 20);
             
  # scalars, arrays and hashes can be
  # inserted at the same time
  push(@stack, ($scalar, @array, %hash)); 
    
  # Updated Stack after 
  # Push operations
  print("\nUpdated Stack: @stack");
  

  输出：

  Original Stack: 1 2 3
  Updated Stack: 1 2 3 scalar a r r a y Geeks 10 for Geeks 20
  

• 使用splice()推送：

  Syntax: splice(@stack, scalar(@stack), 0, list);
  Parameters:

  • splice() function appends the ‘list’ at the end of @stack.
  • THe ‘list’ could be a scalar, an array or a hash.

  例子：

  #!/usr/bin/perl
    
  # Intitialising the Stack
  @stack = (1..3);
    
  # Original stack
  print "Original Stack: @stack";
    
  # Scalar to be pushed
  $scalar = "scalar";
    
  # Array to be pushed
  @array = ("a", "r", "r", "a", "y");
    
  # Hash to be pushed
  %hash = ("Geeks" => 10, 
           "for Geeks" => 20);
    
  # scalars, arrays and hashes can be
  # inserted at the same time
  splice(@stack, scalar(@stack), 0, 
         ($scalar, @array, %hash));
           
  # Updated Stack after 
  # Push operations
  print("\nUpdated Stack: @stack");
  

  输出：

  Original Stack: 1 2 3
  Updated Stack: 1 2 3 scalar a r r a y Geeks 10 for Geeks 20
  

从堆栈中弹出元素

可以使用 pop()函数或 splice()函数来完成弹出。

• 使用pop() 弹出：

  Syntax: $popped_element = pop(@stack);
  Parameters:

  • pop() function returns the popped element.
  • $popped_element contains the element popped from the stack.

  例子：

  #!/usr/bin/perl
    
  # Intitialising the Stack
  @stack = (1..3);
    
  # Original stack
  print "Original Stack: @stack";
    
  # Topmost element i.e. 3 is 
  # removed and returned
  $popped_element = pop(@stack); 
    
  # Printing popped element
  print "\nPopped element: $popped_element";
           
  # Updated Stack after 
  # Pop operation
  print("\nUpdated Stack: @stack");
  

  输出：

  Original Stack: 1 2 3
  Popped element: 3
  Updated Stack: 1 2
  

  • 如果堆栈为空，则返回undef 。 undef 类似于Java中的 NULL 和Python中的 None 。但是，不会引发错误。

    例子：

    #!/usr/bin/perl
      
    # Creating a Stack
    @stack;
      
    # undef is returned since the 
    # stack is empty. 
    # No error is raised.
    $popped_element = pop(@stack); 
      
    # Printing popped element
    # Since it contains no value,
    # hence a blank space is returned
    print "Popped element: $popped_element";
    

    输出：

    Popped element: 
    

• 使用splice():弹出

  Syntax: $popped_element=splice(@stack, -1);
  Parameters:

  • splice() function removes the last element of the stack and returns it.
  • $popped_element stores the returned value.

  例子：

  #!/usr/bin/perl
    
  # Intitialising the Stack
  @stack = (1..3);
    
  # Original stack
  print "Original Stack: @stack";
    
  # popping using splice()
  $popped_element = splice(@stack, -1);
    
  # Printing popped element
  print "\nPopped element: $popped_element";
           
  # Updated Stack after 
  # Pop operation
  print("\nUpdated Stack: @stack");
  

  输出：

  Original Stack: 1 2 3
  Popped element: 3
  Updated Stack: 1 2
  

  • 如果堆栈为空，则会引发错误。以下代码引发错误：

    use warnings;
    #!/usr/bin/perl
      
    use warnings;
      
    # Creating a Stack
    @stack;
      
    # popping using splice()
    # An error is raised here
    $popped_element = splice(@stack, -1); 
      
    # Printing popped element
    print "\nPopped element: $popped_element";
             
    # Updated Stack after 
    # Pop operation
    print("\nStack: @stack");
    

    运行时错误：

    Useless use of a variable in void context at /home/59c7c19979aa9e46564cd145d5fe5601.pl line 6.
    Modification of non-creatable array value attempted, subscript -1 at /home/59c7c19979aa9e46564cd145d5fe5601.pl line 10.