Medium
Interview Brain Teasers
Brain teasers commonly useful for technical and job interviews.
Interview Brain Teasers Puzzles
Hard
You have 9 identical-looking balls and one is heavier. What is the minimum number of balance-scale weighings needed to find it?
Medium
An interviewer gives you two ropes. Each rope takes exactly one hour to burn, but they do not burn at a uniform rate. How can you measure exactly 30 minutes?
Hard
You have a building with 100 floors and two identical glass balls. You need to determine the highest floor from which a ball can be dropped without breaking, while minimizing the worst-case number of drops. What is the classic strategy based on?
Medium
You have 8 identical-looking balls and one is heavier. What is the minimum number of balance-scale weighings needed to guarantee finding it?
Medium
Why are manhole covers usually round rather than square?
Hard
You have 10 bags of coins. One entire bag contains coins that are 1 gram heavier than normal. With one weighing on a precise digital scale, how can you identify the defective bag?
Medium
A clock is losing time at a constant rate. It loses 2 minutes every hour. If it is correct at 8 AM, what will it show at 6 PM?
Hard
You have 25 horses and can race only 5 horses at a time. There is no stopwatch; you only know the finishing order in each race. What is the minimum number of races needed to determine the three fastest horses?
Medium
You have a bucket that holds exactly 10 litres and another that holds exactly 7 litres. Without markings, can you measure exactly 3 litres?
Hard
A company has 100 employees. Exactly one employee is taller than every other employee. Without measuring heights, what type of comparison strategy minimizes the number of pairwise comparisons needed to identify the tallest employee?
Medium
You have 10 identical batteries, but 2 are dead. A device requires two working batteries. What is the minimum number of pairs you need to test in the worst case to guarantee finding a working pair?
Hard
You are asked in an interview: A room contains 100 people. At least two people in the room must share the same birthday. What is the minimum number of people required to guarantee this?
Medium