Guide to High School Computer Science
  • 💻Introduction
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    • 🍎Python Basics
      • What is Python?
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      • Working with Numbers
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      • [EXTRA] Python Style Guide
    • ⏮️Iterations
      • Introduction to While Loops
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      • Introduction to For Loops
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      • Strings
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      • Functions
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      • How to Save Text to an External File
      • Reading CSV in Python
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    • 🔨Basic Python Projects
      • Basic Calculator
        • Improving the calculator
        • Exercise Set 1
        • Exercise Set 2
        • 💎Streamlit Application #1
      • Basic Password Generator
        • Exercise Set 3
        • Exercises Related to Math
        • 💎Streamlit Application #2
      • A To-Do Task List
    • ⏳Introduction to Algorithmic Thinking
      • Big-O Notation
      • Basic Algorithms
        • Linear Search
        • Binary Search
        • Basic Sorting Algorithms
      • Recursion
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      • Greedy Algorithm
        • Time on Task (CCC 2013 J4)
        • Dijkstra’s Algorithm
      • Divide and Conquer
        • Merge Sort
      • Dynamic Programming
    • 🤯Object Oriented Programming
      • Class & Objects (Definitions)
      • OOP in Python
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      • Inheritance & Overriding
      • Override Magic Methods
      • Case Study: 2D Vectors
      • Case Study: Deck of Cards
      • Exercise
      • Abstract Data Types
      • Case Study: Static 1D Array From Java
    • Competitive Programming
      • Is This Sum Possible?
        • Is the dataset sorted?
        • Searching for a value
        • Determine if the difference between an integer from the array and the target value exists
        • Sorting Algorithms
        • Using Two Pointers
      • Two Sum - LeetCode
        • Generate all possible pairs of values
        • Subtract each value from the target, see if the difference exists in the list
      • Longest Common Prefix - LeetCode
        • Compare all possible prefixes
        • Create the longest common prefix with the direct neighbour
      • Length of Last Word - LeetCode
        • Compare all possible prefixes
      • Where can I go from one point to another?
      • Sample Outline
    • IB Recipe Book
  • 💾Python & Databases
    • Intro to Databases & Data Modeling
      • Common Data Types in SQL
      • Introduction to ERDs
      • Primary Keys and Foreign Keys
      • Database Normalization
    • What is SQL?
      • Getting Started
      • SELECT Queries
        • Selection with Conditions
        • Selection with Fuzziness
        • Selection and Sorting in Order
        • Selection without Duplicates
        • Selection with Limited Number of Outputs
      • AGGREGATE Queries
        • Counting Rows
        • Sum, Average, Min/Max Queries
        • Working with Aggregate Queries
        • Power of using Groups
        • Exercise
      • Interacting with Multiple Table
      • Inserting Data
      • External Resource
  • ☕Java Essentials
    • Basics
      • Starting Java
      • Data & Variables
      • Handling User Inputs & Type Conversion
      • Arithmetic
      • IPO Model
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      • Exercise Questions
    • Conditionals
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      • Compare Strings
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      • If Else Statements
      • Making Multiple Decisions
      • Using Switch
      • Flowchart Symbols
      • Exercise Questions
    • Iterations
      • While Loops
      • For Loop
      • Exercises
    • Java Type Casting
    • Strings
      • Common String Practices
      • String Formatting
      • Java Special Characters
    • Collection
      • Arrays
      • For Each Loop
      • ArrayList
      • Exercise Questions
    • Static Methods
      • (Aside) Clearing your Console
    • Randomness in Java
    • Delayed Output in Java
    • Java Output Formatting
    • Java Style Guide
  • 🛠️JavaScript Programming
    • Our Programming Editor & Workflow
      • Hello, world!
      • Commenting & Variables
      • Data in JavaScript
      • Operators
      • String Formatting
      • Getting User Input
    • JavaScript Exercise Set 1
    • Making Decisions
      • Comparing Values
      • Combining Boolean Comparisons
      • Creating Branches
    • JavaScript Exercise Set 2
    • While Loops
      • Infinite While Loop
      • While Loops and Numbers
      • While Loops and Flags
      • While loops w/ Strings
    • JavaScript Exercise Set 3
    • Subprograms & Functions
      • Creating a Function in JavaScript
      • Function with Input and Assignable Output
    • JavaScript Exercise Set 4
  • 💾Topics in CS
    • Computer Environments & Systems
      • Computer Components
        • In-depth Explanations
      • File Maintenance
      • Computer & Safety
      • Software Development
      • Bits & Binary
    • Careers related to Computer Science
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On this page
  • Goal
  • Problem Constraints
  • Problem Requirement Breakdown
  • Possible Solutions
  • Connected Readings
  1. Python Programming
  2. Competitive Programming

Two Sum - LeetCode

PreviousUsing Two PointersNextGenerate all possible pairs of values

Last updated 10 months ago

Goal

Our goal in this chapter is to analyze a competitive programming problem to breakdown the requirements for a solution.

Given an array of integers nums and an integer target, return indices of the two numbers such that they add up to target.

You may assume that each input would have exactly one solution, and you may not use the same element twice.

You can return the answer in any order.

// Sample Runs
Example 1:

Input: nums = [2,7,11,15], target = 9
Output: [0,1]
Explanation: Because nums[0] + nums[1] == 9, we return [0, 1].
Example 2:

Input: nums = [3,2,4], target = 6
Output: [1,2]
Example 3:

Input: nums = [3,3], target = 6
Output: [0,1]

Problem Constraints

Constraints (what our possible test cases will be):

  • Size constraints of the number of integers in the array -> 2 <= nums.length <= 104

  • Each individual integers will be within this range -> -109 <= nums[i] <= 109

  • The target value will be an integer within this range -> -109 <= target <= 109

  • Only one valid combination of two distinct elements (item located at an index) will result to the target.

Problem Requirement Breakdown

    • A list of integers (we must assume that it will be unsorted)

    • An integer target value

  • through the given list of integers and create a total sum based on a unique pair of integers

  • Create a list with the specific indices that adds up to the given target

Possible Solutions

  1. Generate all possible pairs of values

  • If we have all pairs of values, we can create a sum from each pair to compare it with the target.

  • The indices that generated the pair that totals to the target will be our answer

  1. Subtract each value from the target, see if the difference exists in the list

  • Since a sum is a result of two operands added together, we can express it as -> x + y = sum

  • By rearranging the equation, we can also express it as -> y = sum - x

  • If we have the sum set to our given target value, and let x be represented by each individual values in our list, we can generate the y value

    • Each time we generate the y value, we can search the list if the y value exists in the list

    • If the value exists, the index of x and y will be our pair that generated our desired target value

Connected Readings

Create a that can take two arguments:

Functions ()

Loops ()

List ()

🐍
The Problem
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