Welcome back to 'Unlocking Algorithms'! In this section, we delve into two fundamental data structures that underpin many efficient algorithmic solutions: Stacks and Queues. Understanding these structures is like learning the alphabet before writing a novel – essential for clarity and precision in your algorithmic thinking.
At their core, stacks and queues are linear data structures, meaning their elements are arranged in a sequential order. The key differentiator lies in how elements are added and removed, dictated by specific access principles. These principles, LIFO (Last-In, First-Out) for stacks and FIFO (First-In, First-Out) for queues, are crucial for understanding their behavior and applications.
Stacks: The LIFO Principle
Imagine a stack of plates. You can only add a new plate to the top, and when you need a plate, you take it from the top. The last plate you put on is the first one you take off. This is the essence of the Last-In, First-Out (LIFO) principle. In programming, a stack operates similarly. The primary operations are 'push' (adding an element to the top) and 'pop' (removing the element from the top).
graph TD; A(Top) --> B(Element 2); B --> C(Element 1); C --> D(Bottom);
A common use case for stacks is function call management. When one function calls another, the current function's state is 'pushed' onto the call stack. When the called function finishes, its state is 'popped' off, and execution resumes from where it left off. This 'undo' functionality in many applications also leverages the LIFO nature of stacks.
class Stack {
constructor() {
this.items = [];
}
push(element) {
this.items.push(element);
}
pop() {
if (this.isEmpty()) {
return 'Stack is empty';
}
return this.items.pop();
}
peek() {
return this.items[this.items.length - 1];
}
isEmpty() {
return this.items.length === 0;
}
size() {
return this.items.length;
}
}Queues: The FIFO Principle