{"componentChunkName":"component---src-templates-blog-post-jsx","path":"/blog/valid-sudoku-algo-leetcode/","result":{"data":{"site":{"siteMetadata":{"name":"Huzaifa Rasheed","title":"Huzaifa Rasheed","description":"Software Engineer","about":"\n Hey, I'm Huzaifa.\n

\n Engineer by trade, builder by instinct - I believe in owning my stack, shipping fast, and occasionally running on chai (tea) and stubbornness. I work best in that sweet spot between deep focus and fast feedback - solo or in sync with a good team.\n

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\n Outside work, I'm into long walks, pixel-perfect headshots in FPS games (eventually... maybe), plants I probably overwater, and the occasional \"classified\" hobby to stay curious.\n

\n Reach out anytime - my digital door's always open. 👋\n ","twitter":"https://twitter.com/huzRasheed","github":"https://github.com/huzaifa-99","linkedin":"https://www.linkedin.com/in/huzaifa-rasheed/","devto":"https://dev.to/huzaifa99","stackoverflow":"https://stackoverflow.com/users/12579290/huzaifa","leetcode":"https://leetcode.com/rhuzaifa","discord":"https://discordapp.com/users/rhuzaifa","email":"dev@rhuzaifa.com","projects":[{"name":"FFMpeg Web","description":"An experimental browser-based terminal that runs FFmpeg using WebAssembly, enabling media processing directly in the browser.","link":"https://ffmpeg-web.rhuzaifa.com/","github":"https://github.com/huzaifa-99/ffmpeg-web"},{"name":"Feed base 2","description":"A mini browser game where players manipulate 4-bit binary blocks to match target BCD values - part puzzle, part binary logic trainer.","link":"https://feedbase2.rhuzaifa.com/","github":"https://github.com/huzaifa-99/feed-base-2"},{"name":"Fabric browser extension","description":"A Chrome extension that injects engineered Fabric prompts directly into the ChatGPT interface for enhanced workflow automation.","link":"https://github.com/huzaifa-99/fabric-browser-extension","github":"https://github.com/huzaifa-99/fabric-browser-extension"},{"name":"Pure Cinema","description":"An experimental, tongue-in-cheek text-to-video generator that stitches together footage, synthesized voiceovers, and background music with a Node.js + ffmpeg pipeline. Not quite Hollywood, but it renders.","link":"https://cinema.rhuzaifa.com","github":null},{"name":"Aria2c Packload","description":"A Bash script for bulk downloading magnet links or torrents using aria2c - optimized for series or list-based transfers.","link":"https://github.com/huzaifa-99/aria2c-packload","github":"https://github.com/huzaifa-99/aria2c-packload"},{"name":"RSS Watchdog","description":"A lightweight Bash script that watches RSS/Atom feeds and compiles a Markdown-based reading checklist for Unix systems.","link":"https://github.com/huzaifa-99/rss-watchdog","github":"https://github.com/huzaifa-99/rss-watchdog"},{"name":"QuoteGen","description":"A quote graphic generator that produces stylized quote images with random selection and a built-in editor for customization.","link":"https://quotegen.rhuzaifa.com/","github":null},{"name":"WebRTC Video Chat","description":"A basic WebRTC-powered app enabling peer-to-peer video and audio calls between two users.","link":"https://webrtc-video-chat.rhuzaifa.com/","github":null}],"experience":null,"skills":[{"name":"Languages & Frameworks","description":"JavaScript, TypeScript, Python, Bash - Frameworks include Node.js, React, Next.js, Vue, React Native, FastAPI."},{"name":"Databases & Storage","description":"PostgreSQL, MySQL, MongoDB - Experience with schema design, indexing, query optimization, and migrations."},{"name":"Cloud & Infrastructure","description":"AWS (EC2, RDS, S3, Lambda), Vercel, Netlify, Heroku - Comfortable with serverless, autoscaling, and cost optimization."},{"name":"DevOps & Tooling","description":"Docker, Git, CI/CD pipelines (GitHub Actions, GitLab CI) - Experience with observability, containerization, and release workflows."},{"name":"Testing & QA Automation","description":"Jest, Playwright, Puppeteer, Selenium - Focus on E2E testing, mocking APIs, and maintaining test coverage."}]}},"markdownRemark":{"id":"cc130fd5-25e8-50ab-841c-9c284a00607c","excerpt":"Repost of https://dev.to/rhuzaifa/valid-sudoku-algo-leetcode-5f3h So the other day I was doing some leetcode and found the Valid Sudoku problem interesting…","html":"
\n

Repost of https://dev.to/rhuzaifa/valid-sudoku-algo-leetcode-5f3h

\n
\n

So the other day I was doing some leetcode and found the Valid Sudoku problem interesting. Also since I had not posted for a long time (missed it 😁), thought why not just write how I solved, so here it goes.

\n

Algorithm (I followed)

\n
    \n
  1. Map over each row of the board, check if row has duplicate numbers
    2. \n
  2. Map over each column of the board, check if column has duplicate numbers
    3. \n
  3. Map over each row of the board, if that row is the start of a unique 3x3 matrix, then create three 3x3 matrices and check for duplicates
    4. \n
\n

We can check for each test case in a single map

\n

Implementation (JavaScript)

\n
/**\n * @param {character[][]} board\n * @return {boolean}\n */\nvar isValidSudoku = function (board) {\n    // map over each row\n    for (let row = 0; row < board.length; row++) {\n        // we will store and check for dup digits\n        const foundRowDigits = [];\n        const foundColDigits = [];\n\n        // map over each column\n        for (let col = 0; col < board.length; col++) {\n            const rowDigit = board[row][col]\n            if (rowDigit !== '.') { // we are ignoring periods '.'\n                // check duplicates in row\n                if (foundRowDigits.includes(rowDigit)) {\n                    // oh uh, dup found -> invalid sudoku\n                    return false\n                }\n\n                foundRowDigits.push(rowDigit) // store row digit for further comparison\n            }\n\n            const colDigit = board[col][row]\n            if (colDigit !== '.') { // we are ignoring periods '.'\n                // check duplicates in row\n                if (foundColDigits.includes(colDigit)) {\n                    // oh uh, dup found -> invalid sudoku\n                    return false\n                }\n\n                foundColDigits.push(colDigit) // store row digit for further comparison\n            }\n        }\n\n\n        if (row % 3 === 0) { // row is the start of 3 3x3 matrices\n            let threeByThreeGrid = [] // we will store grid values to check dups\n            let rowIndex = row\n\n            for (let colIndex = 0; colIndex < 9; colIndex += 3) {\n                // make 3x3 grid by taking a rowIndex and colIndex\n                for (let gridRowIndex = rowIndex; gridRowIndex < rowIndex + 3; gridRowIndex++) {\n                    for (let gridColIndex = colIndex; gridColIndex < colIndex + 3; gridColIndex++) {\n                        const digit = board[gridRowIndex][gridColIndex]\n                        if (digit !== '.') { // we are ignoring periods '.'\n\n                            // check if there are duplicates in a 3x3 matrix\n                            if (threeByThreeGrid.includes(digit)) {\n                                // oh uh, dup found -> invalid sudoku\n                                return false\n                            }\n\n                            threeByThreeGrid.push(digit) // store row digit for further comparison\n                        }\n                    }\n                }\n\n                threeByThreeGrid = [] // reset the grid\n            }\n        }\n    }\n\n    return true // if above test cases passed then sudoku is valid\n};
\n

Time complexity

\n

O(n^2) - We have 2 nested for loops. The 3x3 subgrids only work in certain cases so going for the worst case we have O(n^2)

\n

Space complexity

\n

O(1)

\n

Test Cases

\n
    \n
  1. \n

    A valid sudoku

    \n
    const validSudoku = [\n[\"5\", \"3\", \".\", \".\", \"7\", \".\", \".\", \".\", \".\"],\n[\"6\", \".\", \".\", \"1\", \"9\", \"5\", \".\", \".\", \".\"],\n[\".\", \"9\", \"8\", \".\", \".\", \".\", \".\", \"6\", \".\"],\n[\"8\", \".\", \".\", \".\", \"6\", \".\", \".\", \".\", \"3\"],\n[\"4\", \".\", \".\", \"8\", \".\", \"3\", \".\", \".\", \"1\"],\n[\"7\", \".\", \".\", \".\", \"2\", \".\", \".\", \".\", \"6\"],\n[\".\", \"6\", \".\", \".\", \".\", \".\", \"2\", \"8\", \".\"],\n[\".\", \".\", \".\", \"4\", \"1\", \"9\", \".\", \".\", \"5\"],\n[\".\", \".\", \".\", \".\", \"8\", \".\", \".\", \"7\", \"9\"]\n];\nconsole.log(isValidSudoku(validSudoku)) // true
    \n
    2. \n
  2. \n

    A sudoku with dups in row

    \n
    const sudokuWithRowDups = [\n[\"5\", \"3\", \".\", \".\", \"7\", \".\", \".\", \".\", \"5\"],\n[\"6\", \".\", \".\", \"1\", \"9\", \"5\", \".\", \".\", \".\"],\n[\".\", \"9\", \"8\", \".\", \".\", \".\", \".\", \"6\", \".\"],\n[\"8\", \".\", \".\", \".\", \"6\", \".\", \".\", \".\", \"3\"],\n[\"4\", \".\", \".\", \"8\", \".\", \"3\", \".\", \".\", \"1\"],\n[\"7\", \".\", \".\", \".\", \"2\", \".\", \".\", \".\", \"6\"],\n[\".\", \"6\", \".\", \".\", \".\", \".\", \"2\", \"8\", \".\"],\n[\".\", \".\", \".\", \"4\", \"1\", \"9\", \".\", \".\", \"5\"],\n[\".\", \".\", \".\", \".\", \"8\", \".\", \".\", \"7\", \"9\"]\n]\nconsole.log(isValidSudoku(sudokuWithRowDups)) // false
    \n
    3. \n
  3. \n

    A sudoku with dups in col

    \n
    const sudokuWithColDups = [\n[\"8\", \"3\", \".\", \".\", \"7\", \".\", \".\", \".\", \".\"],\n[\"6\", \".\", \".\", \"1\", \"9\", \"5\", \".\", \".\", \".\"],\n[\".\", \"9\", \"8\", \".\", \".\", \".\", \".\", \"6\", \".\"],\n[\"8\", \".\", \".\", \".\", \"6\", \".\", \".\", \".\", \"3\"],\n[\"4\", \".\", \".\", \"8\", \".\", \"3\", \".\", \".\", \"1\"],\n[\"7\", \".\", \".\", \".\", \"2\", \".\", \".\", \".\", \"6\"],\n[\".\", \"6\", \".\", \".\", \".\", \".\", \"2\", \"8\", \".\"],\n[\".\", \".\", \".\", \"4\", \"1\", \"9\", \".\", \".\", \"5\"],\n[\".\", \".\", \".\", \".\", \"8\", \".\", \".\", \"7\", \"9\"]\n]\nconsole.log(isValidSudoku(sudokuWithColDups)) // false
    \n
    4. \n
  4. \n

    A sudoku with dups in 3x3 matrices

    \n
    const sudokuWith3x3GridDups = [\n[\".\", \".\", \".\", \".\", \"5\", \".\", \".\", \"1\", \".\"],\n[\".\", \"4\", \".\", \"3\", \".\", \".\", \".\", \".\", \".\"],\n[\".\", \".\", \".\", \".\", \".\", \"3\", \".\", \".\", \"1\"],\n[\"8\", \".\", \".\", \".\", \".\", \".\", \".\", \"2\", \".\"],\n[\".\", \".\", \"2\", \".\", \"7\", \".\", \".\", \".\", \".\"],\n[\".\", \"1\", \"5\", \".\", \".\", \".\", \".\", \".\", \".\"],\n[\".\", \".\", \".\", \".\", \".\", \"2\", \".\", \".\", \".\"],\n[\".\", \"2\", \".\", \"9\", \".\", \".\", \".\", \".\", \".\"],\n[\".\", \".\", \"4\", \".\", \".\", \".\", \".\", \".\", \".\"]\n]\nconsole.log(isValidSudoku(sudokuWith3x3GridDups)) // false
    \n
    5. \n
\n
\n

It may not be perfect, and can always be improved. Let me know your thoughts and thanks for reading.

","frontmatter":{"title":"Valid Sudoku Algo - Leetcode","date":"March 21, 2023","description":"Solving the valid sudoku problem on Leetcode"}}},"pageContext":{"slug":"/blog/valid-sudoku-algo-leetcode/","previous":{"fields":{"slug":"/blog/how-to-avoid-default-props-render-trap-in-react/"},"frontmatter":{"title":"How to Avoid Default Props Render Trap in React"}},"next":{"fields":{"slug":"/blog/xcode-caches-ate-my-ssd-how-i-got-80gb-back/"},"frontmatter":{"title":"Xcode Caches Ate My SSD - How I Got 80GB Back"}}}},"staticQueryHashes":["2276319502"]}