Welcome to MindCipher, a social repository of the world's greatest brain teasers, logic puzzles and mental challenges.

Sort by:

All puzzles

 4 Don't Mate in One This problem was first publicized by Karl Fabel, a German chess problemist. Find a move for white that will not result in an immediate checkmate of the black king. Submitted by Aakash Doable 6.6 13 Bit Pair Swap In one line of C or Java, how would you swap every pair of bits in a byte? That is, swap bits 0 and 1, 2 and 3, 4 and 5, 6 and 7. Example: 0110 1010 becomes 1001 0101. Submitted by Ravi Doable 6.6 9 1978 The year 1978 is such that the sum of the first two digits and the latter two digits is equal to the middle two digits, i.e. 19 + 78 = 97. What is the next year (after 1978) for which this is true? Submitted by Ryan Miller Doable 6.6 12 Simple 24 Why is that if p is a prime number bigger than 3, then p^2-1 is always divisible by 24 with no remainder? Submitted by Aakash Doable 6.6 5 The Stealing Mailman This is a fairly simple problem that can cause some people trouble. Kevin and Sophia want to mail high confidential letters between each other. They know that the mailman is crooked and opens the le ... Submitted by Ravi Doable 6.5 19 Going to the Track The London racetrack needs to submit its top three horses to the Kentucky Derby next month in order to compete for a prize. However in a recent electrical storm, all the racetrack's previous race histo ... Submitted by Nikhil Doable 6.2 28 12 Identical Balls You have 12 identical balls. One of them is slightly different in weight than the rest. You have three weighs of a balance scale to determine which ball is different and whether it is heavier or li ... Submitted by Valentin Doable 6.2 3 Power of 2 (Microsoft Interview) Given any number n, using one line of C (using no external libraries or functions) code, determine if n is a power of 2. Return 1 if n is a power of 2 and 0 if not. Submitted by Aakash Doable 6.0 6 Grey Squares Illusion Square A is the exact same shade of gray as square B. It's true, check out the reconstruction. Submitted by Ravi Doable 6.0 3 Tooth Paste, : Profit There are 2 Persons, Who Saves Money. One person Bought a tooth Paste of 100 gms, for Rs. 40. The second person Buys, Two 50 gms for Rs. 20 each. at same shop, the same company of Pastes. No Extra past ... Submitted by Sachin Prabhu Doable 6.0 2 Use your mobile In this puzzle I have given a message in a coded language. try to solve it. Message: 936382004221833200416381004381 Hint is in the title of this puzzle Submitted by Rohan Umesh Doable 6.0 2 What Am I? Give me food, and I will live Give me water, and I will die What am I? Submitted by Aakash Doable 6.0 0 Don't be a Square Shown is a large square made up of four shapes, and a separate square, labeled with an E. Using all five of the shapes (A through E) only once, can you form a second perfect square? Submitted by Aakash Doable 6.0 5 Crazy Google Interview Question You are shrunk to the height of a nickel and your mass is proportionally reduced so as to maintain your original density. You are then thrown into an empty glass blender. The blades will start moving ... Submitted by Valentin Doable 6.0 2 The North Pole Bear Puzzle Reloaded A man walks 1 mile south, then 1 mile east, and finally 1 mile north to find himself in exactly the same position as he started. He is NOT at the north pole, nor does he shoot a bear. Where is he? ... Submitted by Ravi Doable 6.0