100 Doors Puzzle: Parity, Perfect Squares, Divisor Counts
5 min read The 100 Doors Puzzle: Parity, Perfect Squares, and Why Divisor Counts Matter The 100 doors puzzle is a beautiful number-theory […] Read article
Logic Puzzles
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Logic Puzzles
Classic logic puzzles that challenge your reasoning abilities and creative thinking. From river crossing problems to complex constraint satisfaction, these puzzles develop the analytical mindset crucial for technical interviews.
Puzzle Categories:
Constraint satisfaction: Fox-chicken-grain, missionaries and cannibals
Information theory: Card tricks, encoding problems
Optimization: Minimum steps, optimal strategy
Combinatorics: Counting arrangements, permutations
Solution Approaches:
State space search (BFS/DFS)
Backward reasoning
Constraint elimination
Mathematical modeling
Companies: Google, Microsoft, Palantir, Dropbox frequently use logic puzzles to assess problem-solving skills.
Logic Puzzles
Bridge Crossing Puzzle: Four People, One Flashlight, 17 Minutes
5 min read The Bridge Crossing Puzzle: Four People, One Flashlight, 17 Minutes The bridge-crossing puzzle is a classic interview question that appears Read article
Logic Puzzles
Find the Counterfeit Coin: 9, 10, and 12-Coin Variants Explained
5 min read Find the Counterfeit Coin: 10 Coins (or N Coins), One Different, Minimum Weighings Counterfeit coin puzzles are a classic interview Read article
Logic Puzzles
Getting a fair result with an unfair coin
1 min read How can you get a fair coin toss if someone hands you a coin that is weighted to come up Read article
Brain Teasers, Logic Puzzles
100 Doors in a Row
3 min read Problem: you have 100 doors in a row that are all initially closed. you make 100 passes by the doors Read article
Brain Teasers, Data Structures, Dynamic Programming, Logic Puzzles
Red Marbles, Blue Marbles
4 min read Problem: you have two jars, 50 red marbles, 50 blue marbles. you need to place all the marbles into the Read article
Algorithms, Brain Teasers, Logic Puzzles
Bumblebee
3 min read problem: two trains enter a tunnel 200 miles long (yeah, its a big tunnel) travelling at 100 mph at the Read article
Bit Manipulation, Brain Teasers, Logic Puzzles
Daughters’ Ages
3 min read Two MIT math grads bump into each other at Fairway on the upper west side. They haven’t seen each other Read article
Algorithms, Dynamic Programming, Logic Puzzles, String Manipulation
Palindromes
3 min read Problem: this year on October 2, 2001, the date in MMDDYYYY format will be a palindrome (same forwards as backwards).10/02/2001when Read article
Algorithms, Bit Manipulation, Brain Teasers, Logic Puzzles, Math Problems, Recursion
Sum it Up
4 min read Problem: you are given a sequence of numbers from 1 to n-1 with one of the numbers repeating only once. Read article
Brain Teasers, Logic Puzzles
Pirates
6 min read Five pirates have 100 gold coins. they have to divide up the loot. in order of seniority (suppose pirate 5 Read article
Bit Manipulation, Brain Teasers, Logic Puzzles, String Manipulation, System Design
Fog Creek Programmers
5 min read 100 fogcreek programmers are lined up in a row by an assassin. the assassin puts red and blue hats on them. Read article
Bit Manipulation, Brain Teasers, Logic Puzzles
Bad King
3 min read A bad king has a cellar of 1000 bottles of delightful and very expensive wine. A neighbouring queen plots to Read article
Brain Teasers, Logic Puzzles, Microsoft Interview Questions
Bridge
3 min read Problem: this one is a classic that many of you have probably already heard, but all the more reason why Read article
Algorithms, Bit Manipulation, Brain Teasers, Logic Puzzles, Math Problems, System Design
Card Trick Without the Trick
5 min read This is a card trick without the trick. there is no sleight of hand, no tricks up my sleeve, no Read article