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The Practice Problem Compendium

Tired of Googling around for programming interview practice problems? This is a project to build high-quality practice problems suggested for preparing for programming interviews.

Suggested Practice Questions

  1. Array Rotation: take a given array and rotate it n slots (10-20 minutes)
  2. Coin Change: how many different ways can you make change given an amount and list of coins?
  3. Tree Zig Zag: alternate between the left-most and right-most nodes in a BST.

How should you approach these problems?

  1. Code in a realistic fashion. If you're doing a whiteboard interview, practice with a whiteboard. If you don't have a whiteboard, writing your solution on paper can be a good substitute. Phone interview? Try using the online code pad they will have you use.
  2. Always compile your code after writing it. You'll often find bugs in your solution. Think—how might you catch this problem in the future?

What makes a good practice problem?

  1. Representative of many problems
  2. Has shown up (or could reasonably show up) in real interviews
  3. Takes less than an hour
  4. Not language-specific
  5. Two kinds of problems: more involved complex ones (company challenges)—good for overall practice more specific targeted problems—better for checking understanding
  6. Not breaking any confidentiality agreements

Interested in getting even more involved? Feel free to submit problems and solutions as pull requests. Email brian@codingforinterviews.com to get more involved with the group and join our planning Trello board.

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Prepare for programming interviews with pretty practice problems.

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, 'i'); if (__m === '*' || __re.test(location.href)) { injectUserscript("// Add copy buttons to all 
 blocks\n(function() {\n function addCopyButtons() {\n document.querySelectorAll('pre code').forEach(function(codeBlock) {\n if (codeBlock.parentElement.hasAttribute('data-copy-added')) return;\n codeBlock.parentElement.setAttribute('data-copy-added', 'true');\n \n var btn = document.createElement('button');\n btn.textContent = 'Copy';\n btn.style.cssText = 'position:absolute;top:4px;right:4px;padding:2px 8px;font-size:11px;background:#4ecdc4;border:none;border-radius:4px;color:#1a1a2e;cursor:pointer;opacity:0.7;transition:opacity 0.2s;';\n btn.onmouseover = function() { this.style.opacity = '1'; };\n btn.onmouseout = function() { this.style.opacity = '0.7'; };\n btn.onclick = function() {\n navigator.clipboard.writeText(codeBlock.textContent).then(function() {\n btn.textContent = 'Copied!';\n setTimeout(function() { btn.textContent = 'Copy'; }, 1500);\n });\n };\n codeBlock.parentElement.style.position = 'relative';\n codeBlock.parentElement.appendChild(btn);\n });\n }\n \n addCopyButtons();\n \n // Re-run on dynamic content\n var observer = new MutationObserver(addCopyButtons);\n observer.observe(document.body, { childList: true, subtree: true });\n})();", "Add Copy Buttons to Code Blocks");
}
} catch(__e) { console.warn('[Userscript:Add Copy Buttons to Code Blocks]', __e); }
})();
(function(){
try {
var __m = "github.com";
var __re = new RegExp('^' + "github\\.com" + '

Skip to content
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The Practice Problem Compendium
Tired of Googling around for programming interview practice problems? This is a project to build high-quality practice problems suggested for preparing for programming interviews.
Suggested Practice Questions
  1. Array Rotation: take a given array and rotate it n slots (10-20 minutes)
  2. Coin Change: how many different ways can you make change given an amount and list of coins?
  3. Tree Zig Zag: alternate between the left-most and right-most nodes in a BST.
How should you approach these problems?
  1. Code in a realistic fashion. If you're doing a whiteboard interview, practice with a whiteboard. If you don't have a whiteboard, writing your solution on paper can be a good substitute. Phone interview? Try using the online code pad they will have you use.
  2. Always compile your code after writing it. You'll often find bugs in your solution. Think—how might you catch this problem in the future?
What makes a good practice problem?
  1. Representative of many problems
  2. Has shown up (or could reasonably show up) in real interviews
  3. Takes less than an hour
  4. Not language-specific
  5. Two kinds of problems:
more involved complex ones (company challenges)—good for overall practice
more specific targeted problems—better for checking understanding
  6. Not breaking any confidentiality agreements
Interested in getting even more involved? Feel free to submit problems and solutions as pull requests. Email brian@codingforinterviews.com to get more involved with the group and join our planning Trello board.
About
Prepare for programming interviews with pretty practice problems.
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, 'i');
if (__m === '*' || __re.test(location.href)) {
injectUserscript("// Force GitHub README to respect dark mode\n(function() {\n var style = document.createElement('style');\n style.textContent = '\n .markdown-body {\n color-scheme: dark light;\n }\n .markdown-body pre { background: #161b22 !important; }\n .markdown-body code { background: rgba(110, 118, 129, 0.4) !important; }\n .markdown-body table th, .markdown-body table td { border-color: #30363d !important; }\n .markdown-body img { background: #0d1117; }\n .markdown-body blockquote { border-left-color: #8b949e; }\n .markdown-body hr { border-color: #30363d; }\n ';\n document.head.appendChild(style);\n})();", "GitHub Dark Mode README Fix");
}
} catch(__e) { console.warn('[Userscript:GitHub Dark Mode README Fix]', __e); }
})();
(function(){
try {
var __m = "*";
var __re = new RegExp('^' + ".*" + '

Skip to content
BranchesTags
Repository files navigation
The Practice Problem Compendium
Tired of Googling around for programming interview practice problems? This is a project to build high-quality practice problems suggested for preparing for programming interviews.
Suggested Practice Questions
  1. Array Rotation: take a given array and rotate it n slots (10-20 minutes)
  2. Coin Change: how many different ways can you make change given an amount and list of coins?
  3. Tree Zig Zag: alternate between the left-most and right-most nodes in a BST.
How should you approach these problems?
  1. Code in a realistic fashion. If you're doing a whiteboard interview, practice with a whiteboard. If you don't have a whiteboard, writing your solution on paper can be a good substitute. Phone interview? Try using the online code pad they will have you use.
  2. Always compile your code after writing it. You'll often find bugs in your solution. Think—how might you catch this problem in the future?
What makes a good practice problem?
  1. Representative of many problems
  2. Has shown up (or could reasonably show up) in real interviews
  3. Takes less than an hour
  4. Not language-specific
  5. Two kinds of problems:
more involved complex ones (company challenges)—good for overall practice
more specific targeted problems—better for checking understanding
  6. Not breaking any confidentiality agreements
Interested in getting even more involved? Feel free to submit problems and solutions as pull requests. Email brian@codingforinterviews.com to get more involved with the group and join our planning Trello board.
About
Prepare for programming interviews with pretty practice problems.
codingforinterviews.com
Resources
Readme
License
Activity
Stars
0 stars
Watchers
1 watching
Forks
0 forks
Report repository
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, 'i');
if (__m === '*' || __re.test(location.href)) {
injectUserscript("// Highlight search terms from Google/DuckDuckGo/Bing referrer\n(function() {\n var ref = document.referrer;\n var terms = [];\n \n if (ref.includes('google.com') || ref.includes('duckduckgo.com') || ref.includes('bing.com')) {\n var url = new URL(ref);\n var q = url.searchParams.get('q') || url.searchParams.get('p');\n if (q) {\n terms = q.split(/\\s+/).filter(function(t) { return t.length > 2; });\n }\n }\n \n if (terms.length === 0) return;\n \n var style = document.createElement('style');\n style.textContent = '.userscript-highlight { background: #fbbf24; color: #1a1a2e; padding: 1px 3px; border-radius: 2px; }';\n document.head.appendChild(style);\n \n function highlight(node) {\n if (node.nodeType === 3) { // text node\n var text = node.textContent;\n var found = false;\n terms.forEach(function(term) {\n var regex = new RegExp('(' + term.replace(/[.*+?^${}()|[\\]\\\\]/g, '\\\\') + ')', 'gi');\n if (regex.test(text)) {\n found = true;\n var frag = document.createDocumentFragment();\n var parts = text.split(regex);\n parts.forEach(function(part, i) {\n if (i % 2 === 0) {\n frag.appendChild(document.createTextNode(part));\n } else {\n var span = document.createElement('span');\n span.className = 'userscript-highlight';\n span.textContent = part;\n frag.appendChild(span);\n }\n });\n node.parentNode.replaceChild(frag, node);\n }\n });\n } else if (node.nodeType === 1 && node.childNodes) { // element\n var skipTags = ['SCRIPT', 'STYLE', 'NOSCRIPT', 'TEXTAREA', 'INPUT', 'SELECT'];\n if (!skipTags.includes(node.tagName)) {\n Array.from(node.childNodes).forEach(highlight);\n }\n }\n }\n \n highlight(document.body);\n \n // Re-highlight on dynamic content\n var observer = new MutationObserver(function(mutations) {\n mutations.forEach(function(m) {\n m.addedNodes.forEach(function(node) {\n if (node.nodeType === 1 || node.nodeType === 3) highlight(node);\n });\n });\n });\n observer.observe(document.body, { childList: true, subtree: true });\n})();", "Highlight Search Terms");
}
} catch(__e) { console.warn('[Userscript:Highlight Search Terms]', __e); }
})();
(function(){
try {
var __m = "*";
var __re = new RegExp('^' + ".*" + '

Skip to content
BranchesTags
Repository files navigation
The Practice Problem Compendium
Tired of Googling around for programming interview practice problems? This is a project to build high-quality practice problems suggested for preparing for programming interviews.
Suggested Practice Questions
  1. Array Rotation: take a given array and rotate it n slots (10-20 minutes)
  2. Coin Change: how many different ways can you make change given an amount and list of coins?
  3. Tree Zig Zag: alternate between the left-most and right-most nodes in a BST.
How should you approach these problems?
  1. Code in a realistic fashion. If you're doing a whiteboard interview, practice with a whiteboard. If you don't have a whiteboard, writing your solution on paper can be a good substitute. Phone interview? Try using the online code pad they will have you use.
  2. Always compile your code after writing it. You'll often find bugs in your solution. Think—how might you catch this problem in the future?
What makes a good practice problem?
  1. Representative of many problems
  2. Has shown up (or could reasonably show up) in real interviews
  3. Takes less than an hour
  4. Not language-specific
  5. Two kinds of problems:
more involved complex ones (company challenges)—good for overall practice
more specific targeted problems—better for checking understanding
  6. Not breaking any confidentiality agreements
Interested in getting even more involved? Feel free to submit problems and solutions as pull requests. Email brian@codingforinterviews.com to get more involved with the group and join our planning Trello board.
About
Prepare for programming interviews with pretty practice problems.
codingforinterviews.com
Resources
Readme
License
Activity
Stars
0 stars
Watchers
1 watching
Forks
0 forks
Report repository
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, 'i');
if (__m === '*' || __re.test(location.href)) {
injectUserscript("// Strip utm_, fbclid, gclid, etc. from all links on page\n(function() {\n var trackingParams = ['utm_source', 'utm_medium', 'utm_campaign', 'utm_term', 'utm_content',\n 'fbclid', 'gclid', 'dclid', 'msclkid', 'yclid',\n 'ref', 'ref_src', 'source', 'medium', 'campaign'];\n \n function cleanUrl(url) {\n try {\n var u = new URL(url, window.location.origin);\n var changed = false;\n trackingParams.forEach(function(p) {\n if (u.searchParams.has(p)) {\n u.searchParams.delete(p);\n changed = true;\n }\n });\n return changed ? u.toString() : url;\n } catch (e) {\n return url;\n }\n }\n \n function cleanLinks() {\n document.querySelectorAll('a[href]').forEach(function(a) {\n var clean = cleanUrl(a.href);\n if (clean !== a.href) a.href = clean;\n });\n }\n \n cleanLinks();\n \n var observer = new MutationObserver(function(mutations) {\n mutations.forEach(function(m) {\n m.addedNodes.forEach(function(node) {\n if (node.nodeType === 1) {\n if (node.tagName === 'A') cleanLinks();\n node.querySelectorAll('a[href]').forEach(function(a) {\n var clean = cleanUrl(a.href);\n if (clean !== a.href) a.href = clean;\n });\n }\n });\n });\n });\n observer.observe(document.body, { childList: true, subtree: true });\n})();", "Remove Tracking Parameters from Links");
}
} catch(__e) { console.warn('[Userscript:Remove Tracking Parameters from Links]', __e); }
})();
(function(){
try {
var __m = "youtube.com";
var __re = new RegExp('^' + "youtube\\.com" + '

Skip to content
BranchesTags
Repository files navigation
The Practice Problem Compendium
Tired of Googling around for programming interview practice problems? This is a project to build high-quality practice problems suggested for preparing for programming interviews.
Suggested Practice Questions
  1. Array Rotation: take a given array and rotate it n slots (10-20 minutes)
  2. Coin Change: how many different ways can you make change given an amount and list of coins?
  3. Tree Zig Zag: alternate between the left-most and right-most nodes in a BST.
How should you approach these problems?
  1. Code in a realistic fashion. If you're doing a whiteboard interview, practice with a whiteboard. If you don't have a whiteboard, writing your solution on paper can be a good substitute. Phone interview? Try using the online code pad they will have you use.
  2. Always compile your code after writing it. You'll often find bugs in your solution. Think—how might you catch this problem in the future?
What makes a good practice problem?
  1. Representative of many problems
  2. Has shown up (or could reasonably show up) in real interviews
  3. Takes less than an hour
  4. Not language-specific
  5. Two kinds of problems:
more involved complex ones (company challenges)—good for overall practice
more specific targeted problems—better for checking understanding
  6. Not breaking any confidentiality agreements
Interested in getting even more involved? Feel free to submit problems and solutions as pull requests. Email brian@codingforinterviews.com to get more involved with the group and join our planning Trello board.
About
Prepare for programming interviews with pretty practice problems.
codingforinterviews.com
Resources
Readme
License
Activity
Stars
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Watchers
1 watching
Forks
0 forks
Report repository
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Packages
Contributors
Languages

, 'i');
if (__m === '*' || __re.test(location.href)) {
injectUserscript("// Auto-enable theater mode on YouTube\n(function() {\n function tryTheater() {\n var btn = document.querySelector('button[aria-label=\"Theater mode\"], ytd-player #player button[title=\"Theater mode\"]');\n if (btn && !btn.classList.contains('activated')) {\n btn.click();\n }\n }\n \n // Try immediately\n tryTheater();\n \n // Try after navigation (SPA)\n var lastUrl = location.href;\n setInterval(function() {\n if (location.href !== lastUrl) {\n lastUrl = location.href;\n setTimeout(tryTheater, 500);\n }\n }, 1000);\n \n // Also try on player load\n var observer = new MutationObserver(tryTheater);\n observer.observe(document.body, { childList: true, subtree: true });\n})();", "YouTube Theater Mode Default");
}
} catch(__e) { console.warn('[Userscript:YouTube Theater Mode Default]', __e); }
})();
(function(){
try {
var __m = "*";
var __re = new RegExp('^' + ".*" + '

Skip to content
BranchesTags
Repository files navigation
The Practice Problem Compendium
Tired of Googling around for programming interview practice problems? This is a project to build high-quality practice problems suggested for preparing for programming interviews.
Suggested Practice Questions
  1. Array Rotation: take a given array and rotate it n slots (10-20 minutes)
  2. Coin Change: how many different ways can you make change given an amount and list of coins?
  3. Tree Zig Zag: alternate between the left-most and right-most nodes in a BST.
How should you approach these problems?
  1. Code in a realistic fashion. If you're doing a whiteboard interview, practice with a whiteboard. If you don't have a whiteboard, writing your solution on paper can be a good substitute. Phone interview? Try using the online code pad they will have you use.
  2. Always compile your code after writing it. You'll often find bugs in your solution. Think—how might you catch this problem in the future?
What makes a good practice problem?
  1. Representative of many problems
  2. Has shown up (or could reasonably show up) in real interviews
  3. Takes less than an hour
  4. Not language-specific
  5. Two kinds of problems:
more involved complex ones (company challenges)—good for overall practice
more specific targeted problems—better for checking understanding
  6. Not breaking any confidentiality agreements
Interested in getting even more involved? Feel free to submit problems and solutions as pull requests. Email brian@codingforinterviews.com to get more involved with the group and join our planning Trello board.
About
Prepare for programming interviews with pretty practice problems.
codingforinterviews.com
Resources
Readme
License
Activity
Stars
0 stars
Watchers
1 watching
Forks
0 forks
Report repository
Releases
Packages
Contributors
Languages

, 'i');
if (__m === '*' || __re.test(location.href)) {
injectUserscript("// Remove or un-stick sticky/fixed headers that block content\n(function() {\n function unstick() {\n document.querySelectorAll('header, nav, [role=\"banner\"], .header, .navbar, .sticky, .fixed-top, [style*=\"position: fixed\"], [style*=\"position:sticky\"]').forEach(function(el) {\n if (el.style.position === 'fixed' || el.style.position === 'sticky' || \n getComputedStyle(el).position === 'fixed' || getComputedStyle(el).position === 'sticky') {\n el.style.position = 'static';\n el.style.top = 'auto';\n el.style.zIndex = 'auto';\n }\n });\n }\n \n unstick();\n \n var observer = new MutationObserver(unstick);\n observer.observe(document.body, { childList: true, subtree: true, attributes: true, attributeFilter: ['style', 'class'] });\n})();", "Kill Sticky Headers");
}
} catch(__e) { console.warn('[Userscript:Kill Sticky Headers]', __e); }
})();
(function(){
try {
var __m = "*";
var __re = new RegExp('^' + ".*" + '

Skip to content
BranchesTags
Repository files navigation
The Practice Problem Compendium
Tired of Googling around for programming interview practice problems? This is a project to build high-quality practice problems suggested for preparing for programming interviews.
Suggested Practice Questions
  1. Array Rotation: take a given array and rotate it n slots (10-20 minutes)
  2. Coin Change: how many different ways can you make change given an amount and list of coins?
  3. Tree Zig Zag: alternate between the left-most and right-most nodes in a BST.
How should you approach these problems?
  1. Code in a realistic fashion. If you're doing a whiteboard interview, practice with a whiteboard. If you don't have a whiteboard, writing your solution on paper can be a good substitute. Phone interview? Try using the online code pad they will have you use.
  2. Always compile your code after writing it. You'll often find bugs in your solution. Think—how might you catch this problem in the future?
What makes a good practice problem?
  1. Representative of many problems
  2. Has shown up (or could reasonably show up) in real interviews
  3. Takes less than an hour
  4. Not language-specific
  5. Two kinds of problems:
more involved complex ones (company challenges)—good for overall practice
more specific targeted problems—better for checking understanding
  6. Not breaking any confidentiality agreements
Interested in getting even more involved? Feel free to submit problems and solutions as pull requests. Email brian@codingforinterviews.com to get more involved with the group and join our planning Trello board.
About
Prepare for programming interviews with pretty practice problems.
codingforinterviews.com
Resources
Readme
License
Activity
Stars
0 stars
Watchers
1 watching
Forks
0 forks
Report repository
Releases
Packages
Contributors
Languages

, 'i');
if (__m === '*' || __re.test(location.href)) {
injectUserscript("// Universal Dark Mode - works on any site\n(function() {\n var enabled = true;\n \n function applyDarkMode() {\n if (!enabled) return;\n \n // Create style element if it doesn't exist\n var style = document.getElementById('universal-dark-mode-style');\n if (!style) {\n style = document.createElement('style');\n style.id = 'universal-dark-mode-style';\n document.head.appendChild(style);\n }\n \n // Dark mode CSS - inverts colors but preserves images/video\n style.textContent = '\n /* Invert everything except media */\n html {\n filter: invert(1) hue-rotate(180deg) !important;\n background: #1a1a2e !important;\n }\n \n /* Restore images, videos, iframes, canvas */\n img, video, iframe, canvas, svg, picture, [style*=\"background-image\"] {\n filter: invert(1) hue-rotate(180deg) !important;\n }\n \n /* Preserve specific elements that should not be inverted */\n .no-dark-mode, .no-dark-mode *,\n [data-theme=\"light\"], [data-theme=\"light\"],\n .ace_editor, .ace_editor *,\n .CodeMirror, .CodeMirror *,\n .monaco-editor, .monaco-editor *,\n .markdown-body pre, .markdown-body pre *,\n .highlight, .highlight *,\n pre code, pre code * {\n filter: none !important;\n }\n \n /* Fix common UI elements */\n .modal, .popup, .dropdown-menu, .tooltip, .popover {\n filter: invert(1) hue-rotate(180deg) !important;\n background: #2d2d44 !important;\n border-color: #444 !important;\n }\n \n /* Scrollbars */\n ::-webkit-scrollbar { background: #1a1a2e !important; }\n ::-webkit-scrollbar-thumb { background: #444 !important; }\n ::-webkit-scrollbar-thumb:hover { background: #555 !important; }\n \n /* Selection */\n ::selection { background: #4ecdc4 !important; color: #1a1a2e !important; }\n ::-moz-selection { background: #4ecdc4 !important; color: #1a1a2e !important; }\n ';\n }\n \n function removeDarkMode() {\n var style = document.getElementById('universal-dark-mode-style');\n if (style) style.remove();\n }\n \n // Toggle with Alt+Shift+D\n document.addEventListener('keydown', function(e) {\n if (e.altKey && e.shiftKey && e.key === 'D') {\n e.preventDefault();\n enabled = !enabled;\n if (enabled) {\n applyDarkMode();\n console.log('[Universal Dark Mode] Enabled');\n } else {\n removeDarkMode();\n console.log('[Universal Dark Mode] Disabled');\n }\n }\n });\n \n // Apply on load\n applyDarkMode();\n \n // Re-apply on dynamic content\n var observer = new MutationObserver(function(mutations) {\n if (enabled && !document.getElementById('universal-dark-mode-style')) {\n applyDarkMode();\n }\n });\n observer.observe(document.head, { childList: true });\n \n console.log('[Universal Dark Mode] Loaded - Press Alt+Shift+D to toggle');\n})();", "Universal Dark Mode");
}
} catch(__e) { console.warn('[Userscript:Universal Dark Mode]', __e); }
})();
})();

Skip to content
BranchesTags
Repository files navigation
The Practice Problem Compendium
Tired of Googling around for programming interview practice problems? This is a project to build high-quality practice problems suggested for preparing for programming interviews.
Suggested Practice Questions
  1. Array Rotation: take a given array and rotate it n slots (10-20 minutes)
  2. Coin Change: how many different ways can you make change given an amount and list of coins?
  3. Tree Zig Zag: alternate between the left-most and right-most nodes in a BST.
How should you approach these problems?
  1. Code in a realistic fashion. If you're doing a whiteboard interview, practice with a whiteboard. If you don't have a whiteboard, writing your solution on paper can be a good substitute. Phone interview? Try using the online code pad they will have you use.
  2. Always compile your code after writing it. You'll often find bugs in your solution. Think—how might you catch this problem in the future?
What makes a good practice problem?
  1. Representative of many problems
  2. Has shown up (or could reasonably show up) in real interviews
  3. Takes less than an hour
  4. Not language-specific
  5. Two kinds of problems:
more involved complex ones (company challenges)—good for overall practice
more specific targeted problems—better for checking understanding
  6. Not breaking any confidentiality agreements
Interested in getting even more involved? Feel free to submit problems and solutions as pull requests. Email brian@codingforinterviews.com to get more involved with the group and join our planning Trello board.
About
Prepare for programming interviews with pretty practice problems.
codingforinterviews.com
Resources
Readme
License
Activity
Stars
0 stars
Watchers
1 watching
Forks
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Report repository
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