Algorithms 101: What is a Stack

栈是什么？What is a Stack?

A stack is a linear data structure that follows the Last-In-First-Out (LIFO) principle. This means that the last element added to the stack will be the first one to be removed. Stacks are used in various applications, including expression evaluation, backtracking algorithms, and the undo mechanism in text editors.

栈是一种线性数据结构，遵循后进先出 (LIFO) 原则。这意味着最后添加到栈中的元素将是第一个被移除的元素。栈用于各种应用场景，包括表达式求值、回溯算法和文本编辑器中的撤销机制。

栈的基本操作

Basic Operations of a Stack

Push: Adds an element to the top of the stack.

压栈 (Push)：将元素添加到栈的顶部。

In the push operation, a new element is added to the top of the stack. This operation increases the size of the stack by one and positions the new element as the first to be removed in subsequent operations.

在压栈操作中，一个新元素被添加到栈的顶部。此操作将栈的大小增加一，并使新元素成为后续操作中第一个被移除的元素。

stack = []
stack.append(10)  # Push 10 onto the stack
stack.append(20)  # Push 20 onto the stack

Pop: Removes an element from the top of the stack.

出栈 (Pop)：从栈的顶部移除一个元素。

In the pop operation, the element at the top of the stack is removed and returned. This operation decreases the size of the stack by one and makes the next element the new top of the stack.

在出栈操作中，栈顶部的元素被移除并返回。此操作将栈的大小减少一，并使下一个元素成为新的栈顶。

top_element = stack.pop()  # Pop the top element (20)

Peek/Top: Retrieves the top element of the stack without removing it.

查看栈顶 (Peek/Top)：检索栈顶元素，但不移除它。

The peek or top operation allows you to view the element at the top of the stack without actually removing it. This is useful when you need to inspect the most recent item added to the stack.

查看栈顶操作允许您查看栈顶的元素，而无需实际移除它。当您需要检查最近添加到栈中的项时，这非常有用。

top_element = stack[-1]  # Peek at the top element (10)

IsEmpty: Checks if the stack is empty.

是否为空 (IsEmpty)：检查栈是否为空。

The IsEmpty operation checks whether the stack has any elements. This is important for determining if any further pop operations can be performed or if new elements need to be pushed onto the stack.

IsEmpty 操作检查栈是否有任何元素。这对于确定是否可以执行进一步的 pop 操作或是否需要将新元素压入栈中非常重要。

is_empty = len(stack) == 0  # Check if the stack is empty (False)

总结

Conclusion

Stacks are a fundamental data structure that are essential in many computing applications. By understanding and implementing basic stack operations like push, pop, peek, and isEmpty, you can effectively manage and process data in scenarios where order and reversibility are crucial.

栈是一种基本的数据结构，在许多计算应用中至关重要。通过理解和实现诸如 push、pop、peek 和 isEmpty 之类的基本栈操作，您可以在顺序和可逆性至关重要的场景中有效地管理和处理数据。