Stacks — Simple English

76 lessons · Data Structures & Algorithms · Simple English · Beginner Friendly

01 Understanding the Problem: Why We Need LIFO OrderFree Understanding the Problem: Why Order Matters Before learning a new data structure, it helps to first understand the prob… 02 The Stack: A LIFO Data StructureFree Meet the Stack Some problems only make sense when you handle the most recent item first. The last thing you put away is … 03 Key Properties of a Stack: Capacity, Size, and TopFree Key Properties of a Stack Once you understand what a stack is — a pile of items where you always add and remove from the… 04 Stack Operations: Push, Pop, Size, and Top🔒 Stack Operations: Push, Pop, Size, and Top A stack is a simple but strict data store. Think of it like a pile of plates:… 05 How to Build a Stack Using an Array🔒 How to Build a Stack Using an Array A stack is a simple way to store data where you can only add or remove items from on… 06 Building a Stack Class Using an Array🔒 Building a Stack Class Using an Array A stack is a collection where you can only add or remove items from one end, calle… 07 Finding the Size of a Stack🔒 Finding the Size of a Stack A stack is a way to store items where you only add and remove from one end, called the top. … 08 Checking if a Stack is Empty🔒 Checking if a Stack is Empty Sometimes, before you do anything with a stack, you need to ask a simple question: "Is ther… 09 The `top` Operation: Looking at the Top Item of a Stack🔒 Looking at the Top of a Stack A stack is like a pile of plates. You can only touch the plate on top. The top operation l… 10 Pushing an Item onto a Stack🔒 Pushing an Item onto a Stack A stack is a way to store items where you only add and remove from one end, called the top.… 11 The Pop Operation: Removing the Top Item from a Stack🔒 The Pop Operation: Removing the Top Item from a Stack A stack is like a pile of plates. You can only add a plate to the … 12 Designing a Stack Using an Array🔒 Designing a Stack Using an Array A stack is one of the simplest and most useful data structures in programming. The easi… 13 Two Stacks Sharing One Array🔒 Two Stacks Sharing One Array A stack is a simple way to store data where you add and remove items from one end only — li… 14 Building a Stack with a Linked List🔒 Building a Stack with a Linked List A stack is a simple data structure. You can only do two things with it: push (add an… 15 Building a Stack with a Linked List Inside a Class🔒 Building a Stack with a Linked List Inside a Class A stack is a collection where you only add and remove items from one … 16 Finding the Size of a Stack (Linked List Version)🔒 Finding the Size of a Stack A stack often needs to answer one simple question: "How many items are inside me right now?"… 17 Checking if a Stack is Empty (Linked List Version)🔒 Checking if a Stack is Empty When you work with a stack, you often need to ask one simple question first: "Is there anyt… 18 Accessing the Top of the Stack🔒 Accessing the Top of the Stack A stack is like a pile of plates. You always add a new plate on top, and the plate you ca… 19 Pushing an Item onto a Stack (Linked List Version)🔒 Pushing an Item onto a Stack (Linked List Version) A stack is like a pile of plates. You add a new plate on top, and you… 20 The Pop Operation: Removing the Top Item from a Stack🔒 The Pop Operation: Removing the Top Item from a Stack A stack lets you add and remove items from only one end — the top.… 21 Designing a Stack Using a Linked List🔒 What is a Stack? A stack is a simple way to store items where you can only add or remove from one end — the top. Think o… 22 Understanding the Infix Notation🔒 Understanding the Infix Notation Computers were first invented to do math much faster than humans could by hand. But bef… 23 Postfix Notation: Writing the Operator After the Operands🔒 Postfix Notation (Reverse Polish Notation) When you write math like 2 + 3, you put the + sign between the two numbers. T… 24 Prefix Notation (Polish Notation): Operator First🔒 Prefix Notation: Putting the Operator First When we write math the normal way, we put the operator (like +, -, , /) betw… 25 Evaluating Postfix Expressions Using a Stack🔒 Evaluating Postfix Expressions Using a Stack When we do math by hand, we write expressions like 5 + 2. The operator (the… 26 Evaluating a Postfix Expression Using a Stack🔒 Evaluating a Postfix Expression When you write math the normal way, you put the operator between the two numbers. For ex… 27 Evaluating Prefix Expressions Using a Stack🔒 Evaluating Prefix Expressions Using a Stack When we write math, we usually put the operator between the two numbers, lik… 28 Evaluating a Prefix Expression🔒 Evaluating a Prefix Expression When you do math, you usually write the operator between two numbers, like 6 / 3 or 8 + 2… 29 Evaluating an Infix Expression🔒 Evaluating an Infix Expression When you write a normal math expression like (1+2)(3/4), you are using something called i… 30 Converting Postfix to Prefix Using a Stack🔒 Converting Postfix to Prefix Using a Stack When we write a math expression like A + B, the operator + sits between its t… 31 Converting a Postfix Expression to a Prefix Expression🔒 Converting a Postfix Expression to a Prefix Expression When we write math like 7 + 3, the operator (+) sits between the … 32 Converting a Postfix Expression Back to Infix Using a Stack🔒 Converting a Postfix Expression Back to Infix You have probably written math like 5 + 2 your whole life. The operator (t… 33 Converting a Postfix Expression to Infix🔒 Converting a Postfix Expression to Infix When we write math, we usually put the operator between the two numbers, like 5… 34 Converting Prefix Notation to Postfix Notation Using a Stack🔒 Converting Prefix to Postfix Using a Stack In an expression, we can write the operator in three different places. In pre… 35 Convert a Prefix Expression to a Postfix Expression🔒 Convert Prefix to Postfix When we write math, we usually put the operator between the two numbers, like 7 - 8. This ever… 36 Converting a Prefix Expression to Infix Using a Stack🔒 Converting a Prefix Expression to Infix Two ways to write the same math We usually write math with the operator sitting … 37 Converting a Prefix Expression to Infix🔒 Converting a Prefix Expression to Infix When we write math, we usually put the operator between the two numbers, like 7 … 38 Converting Infix Expressions to Postfix Using a Stack🔒 Converting Infix Expressions to Postfix Using a Stack When we write math, we put the operator between the two numbers, l… 39 Converting Infix Expressions to Postfix🔒 Converting Infix Expressions to Postfix When we write math, we usually put the operator between the two numbers. For exa… 40 Converting Infix Expressions to Prefix Using a Stack🔒 Converting Infix to Prefix When we write math like 5 2 + 6 / 3 + 3, the operator sits between its two numbers. This ever… 41 Converting an Infix Expression to Prefix Notation🔒 Converting an Infix Expression to Prefix Notation When we write math, we usually put the operator (like +, -, , /) betwe… 42 The Reversal Pattern: Using a Stack to Reverse a Sequence🔒 The Reversal Pattern: Using a Stack to Reverse a Sequence A quick reminder about how data is stored In simple data struc… 43 The Reversal Pattern: Reversing a String with a Stack🔒 The Reversal Pattern Some problems share the same shape, even when they look different on the surface. Once you learn to… 44 Stack Inversion: Reversing a Stack🔒 Stack Inversion: Reversing a Stack A stack is a simple way to store things, one on top of another — just like a pile of … 45 Reverse a String Using a Stack🔒 Reverse a String Using a Stack Imagine you have a word like abcdefgh, and you want to flip it so the last letter comes f… 46 Reverse an Array Using a Stack🔒 Reverse an Array Using a Stack In this lesson, we learn how to flip an array so that its elements come out in the opposi… 47 Reversing the Order of Words in a String🔒 Reversing the Order of Words in a String Imagine you have a sentence made of several words. Your job is to flip the orde… 48 The Previous Closest Occurrence Pattern: Finding the Previous Greater Item with a Stack🔒 The Problem Imagine you have a row of numbers. For each number, you want to find the previous greater item — the closest… 49 The Previous Closest Occurrence Pattern: Finding the Previous Greater Item with a Stack🔒 The Previous Closest Occurrence Pattern Some problems ask you to look backwards in a list and answer a simple-sounding q… 50 Preceding Superior Element: Finding the First Bigger Number on the Left🔒 Preceding Superior Element Imagine you are standing in a line of people, and you want to know: who is the first person t… 51 Preceding Inferior Element: Finding the First Smaller Number to the Left🔒 Preceding Inferior Element This is a classic problem that helps you practice thinking about an array from left to right … 52 Preceding Superior Element in a Circular Array🔒 Finding the First Bigger Number on the Left (Circular) Imagine you have a list of numbers. For each number, you want to … 53 Preceding Inferior Element in a Circular Array🔒 Finding the Preceding Inferior Element in a Circular Array This lesson is about a common type of array problem. Don't wo… 54 The Next Closest Occurrence Pattern: Finding the Next Greater Element with a Stack🔒 The Next Closest Occurrence Pattern Imagine you are standing in a line of people of different heights, and for each pers… 55 The Next Closest Occurrence Pattern (Next Greater / Smaller Element)🔒 The Next Closest Occurrence Pattern Imagine you are standing in a line of people of different heights. You look to your … 56 Succeeding Superior Element: The First Bigger Number to the Right🔒 What the problem is asking You are given two lists of numbers, called arr1 and arr2. Every number in arr2 also appears s… 57 Succeeding Inferior Element: Finding the Next Smaller Number to the Right🔒 Succeeding Inferior Element This lesson is about a common kind of array problem: for a given number, we want to find the… 58 Next Greater Element in a Circular Array🔒 Next Greater Element in a Circular Array Imagine you are standing in a line of people, and each person has a height. For… 59 Finding the Next Smaller Element in a Circular Array🔒 Finding the Next Smaller Element in a Circular Array Imagine you are standing on a number and you want to find the first… 60 Finding the Next Bigger Value for Each Node in a Linked List🔒 Succeeding Superior Nodes The setup Imagine a linked list: a chain of boxes (called nodes) where each box holds a number… 61 Trapping Rain Water: How Much Water Can the Bars Hold?🔒 Trapping Rain Water Imagine a row of walls of different heights standing side by side, with no gaps between them. Each w… 62 Largest Rectangle in a Histogram🔒 Largest Rectangle in a Histogram What is a histogram? A histogram is just a row of bars standing next to each other. Eac… 63 The Sequence Validation Pattern: Using a Stack to Check Start and End Events🔒 The Sequence Validation Pattern Some problems give you a list of items that are connected in pairs. Each pair has a star… 64 Spotting and Solving Sequence Validation Problems (Valid Brackets)🔒 Spotting and Solving Sequence Validation Problems Some problems give you a list of things that happen in order, and a se… 65 Valid Parentheses: Checking if Brackets are Balanced🔒 Valid Parentheses: Checking if Brackets are Balanced Imagine you are writing some math or code, and you use brackets lik… 66 Minimum Edits to Make Parentheses Valid🔒 Minimum Edits to Make Parentheses Valid Imagine you are typing some brackets and you make a few mistakes. Some brackets … 67 Detecting Redundant Parentheses in an Expression🔒 Detecting Redundant Parentheses Parentheses in a math expression are like brackets that group things together. They tell… 68 Balanced Span: Finding the Longest Balanced Parentheses Substring🔒 Balanced Span: The Longest Stretch of Matching Parentheses Imagine you have a line of opening brackets ( and closing bra… 69 The Linear Evaluation Pattern: Using a Stack to Process a Sequence with Triggers🔒 What problem are we solving? Sometimes you are given a list of items, one after another, and you must process them from … 70 Identifying the Linear Evaluation Pattern (Simplify a Linux Path with a Stack)🔒 Identifying the Linear Evaluation Pattern Earlier you learned a technique called linear evaluation. It is a way to solve… 71 Simplify a UNIX File Path (Canonical Path)🔒 Cleaning Up a Messy File Path In UNIX-style systems (like Linux and macOS), every file and folder has an address called … 72 Bracketed Reversal: Flipping the Letters Inside Brackets🔒 Bracketed Reversal Imagine you have a sentence written on paper, and someone draws square brackets around a few words. T… 73 String Expansion: Decoding a k-Encoded String🔒 String Expansion: Decoding a k-Encoded String Sometimes we store text in a short, "packed" form to save space, and later… 74 Formula Parsing: Reading a Chemical Formula String🔒 Formula Parsing: Counting Atoms in a Chemical Formula Imagine someone hands you a chemical formula written as text, like… 75 Design a Min Stack: Getting the Smallest Value Instantly🔒 Design a Min Stack A stack is a simple way to store data where you only ever add or remove from the top. Think of a pile… 76 Design a Max Stack: Get the Maximum in O(1) Time🔒 Design a Max Stack A stack is a simple data structure where you add and remove items from the same end, called the top. …