Free Online Sudoku Solver and Puzzle Generator

Overview

A comprehensive, browser-based Sudoku application that functions as both an interactive puzzle player and a robust mathematical solver. The tool allows users to input their own puzzles to solve or generate fresh, valid Sudoku boards across varying difficulty levels (Easy, Medium, Hard, Expert).

Core Features

• Interactive 9x9 Grid: A fully responsive grid using standard CSS grid layout. It includes visual sub-grid separation (3x3 blocks).
• Puzzle Generator: An integrated algorithm to generate valid, unique Sudoku puzzles. Difficulty levels are determined by the number of pre-filled clues provided.
• Sudoku Solver: An intelligent solver engine that validates user input and computes the correct solution for any solvable Sudoku board.
• Virtual Numpad: An on-screen interface for selecting numbers to place in cells, ensuring compatibility with touchscreens and desktops.
• Input Validation: Real-time highlighting of conflicting numbers (e.g., repeating digits in a row, column, or 3x3 box).
• Utility Controls: Buttons to 'Clear Board', 'Solve Current', 'New Game', and 'Undo Last Move'.

Technical Design

• Frameworks: Pure Vanilla JavaScript, HTML5, and CSS3. No frameworks, libraries, or build processes. CDN access for math/utility libraries is permitted if strictly necessary.
• Self-Contained: The final application must be a single HTML file containing all logic, styles, and markup. It must be portable and work perfectly when embedded in a sandboxed iframe.
• Responsiveness: Fluid layout that adapts to all screen sizes, from mobile phones to desktops. The grid must remain square and legible regardless of viewport width.
• Design Aesthetic: Professional, minimalist light-mode aesthetic. Use a clean color palette (off-white background #FFFFFF, dark gray borders #333333, light blue focus states #E3F2FD, error state red #FFEBEE).
• Constraints Compliance:
  • Strictly No Dark Mode: The UI must be high-contrast light mode only.
  • No Footer: The layout must end immediately after the grid and control area; no footer content is permitted.

Interaction & Animations

• Micro-interactions: Use CSS transitions for button hover states (opacity change) and grid cell selection (subtle background color changes).
• Visual Feedback: Numbers placed by the user should appear with a crisp, sans-serif font. Numbers placed by the 'Solve' function should appear in a distinct color (e.g., deep blue) to differentiate them from user input.