Top 10 Puzzles, Riddles, Logical, and Lateral Thinking Questions for Programming Job Interviews

Puzzles, riddles, logical questions, and lateral thinking questions are an integral part of any programming job interviews. I missed to include some puzzles when I shared my list of top 30 programming interview questions earlier, and a couple of my friends requested to share some puzzles as well. These puzzles and lateral thinking questions are mostly collected from various Java programming interviews on Investment banks, but they are equally useful for any programming job interviews. I have seen more puzzles and logical questions at the junior level i.e. 2 to 4 years.


These kinds of puzzles, if asked at the beginning of the interview, can make or break the interview. It’s not easy to solve them, especially when you see them the first time, but what is surely not to do is give up without a trial, even if you can't think of an answer, try to show a rational approach. Remember it's OK if you don't answer any puzzle question, but your approach towards unknown problem get noticed.

At the same time, lateral thinking questions offers several answers, and you can give your own explanation as well, but make sure it must look genuine and seems logical. 

Puzzles and riddles also form a big chunk of Microsoft and Google Interview questions as well, and they are some really nasty and tough to answer. Anyway, I have not provided answers to these puzzles and logical questions, so that you can at least give it a try. 

Immediate answers kill the purpose of puzzles and riddles, and it's fun to solve them by yourself. By the way, you can easily find answers to these puzzles using Google, as they have asked numerous times on various programming interviews on software and technology companies.

10 Best Puzzles, Riddles, Logical and Lateral thinking question

Here is my list of 10 riddles, puzzles, logical and lateral thinking questions. Try to solve it by yourself before searching for answers in Google, (I have provided answer at the end of the article) they are not that tough or difficult. Easy answers spoil the purpose of puzzles, so don’t look at them, until you are going for an interview the very next day.

1. 27 Coin Problem

There are 27 coins and a two-pan balance. All coins has same weight except for one, which is heavier than all others. All coins looks identical. What is the minimum number of weighing required to certainly find out heavier coin?

2. Two Stick Problem

There are two sticks that take one hour to burn from one end to other. The sticks do not burn at a constant rate i.e. some part may burn faster than others. You need to measure 45 minutes by using these two sticks and a lighter.

3. Railway Tunnel Problem

Two persons are walking into a railway tunnel. Upon crossing 2/3rd of the tunnel, they saw a train is coming from the opposite direction. Each person ran for a different end of tunnel with the speed of 10 km per hour. Fortunately, both persons escaped from the tunnel just right time i.e.. at the time train would have run through them. Assuming train was running with a constant speed and both persons reacted immediately, Find out speed of train.

4. Three Switches Problem

There are three switches outside of a closed room to operate three different light bulb inside the room. You can only go into the room once and you need to determine which switch belongs to which bulb. Just to make it clear, room is perfectly locked and its not possible to determine whether lights are on from outside the room.

5. Jar with Marbles Problem

You have 10 Jars filled with marbles. Each marble weighs 10 gm, except one Jar which contains defective marbles which weigh 9 gm. Given a scale to weigh, How do you find a Jar with defective marbles in just one measurement. Here the scale is a modern-day electronic scale to measure weight.

6. Shooting Wife Problem

A person shoots her wife. Then holds her under water for 5 minutes. Finally, he hangs her. But after 10 minutes they both go out together and enjoy a wonderful dinner together. How can this be?

7. Father and Son Accident Problem

A father and son are going in a car and suddenly their car met an accident. Father died on the spot but the child was rushed to the hospital. When he arrives in the hospital, the doctor says, "I can't operate on this child, he is my son!" How can this be?

8. 5 Liter and 3 Liter Jug Problem

You have a 5-liter Jug and a 3-liter Jug and an unlimited supply of water. You need to measure exactly 4 liters of water but there is no measuring instrument or cup. Also, Jugs are oddly shaped and don't contain any marks.

9. Crossing the bridge Problem

There are Four people who need to cross the bridge during the night. The bridge can hold the weight of two people at a time and can not be crossed without a torch. Each person walks at a different speed, first can cross the bridge in 1 minute, second in 2 minutes, third in 5 minutes and fourth take 10 minutes to cross the bridge. If two persons go together, they walk at the speed of the slower person. What is the least amount in which all four people cross the bridge?

10. Father and Son Age problem

A person's age is many days as his father's age in weeks and as many months as his grandfather's age in years. If you combine the age of all three it comes to 120 years. What is the age of all three?

Puzzle and Riddle Solutions

Here are the solution of all these question I have shared above: 

Solution of 27 Coin Problem

To definitively identify the one heavier coin among 27 indistinguishable coins using only a two-pan balance, a strategic approach can achieve this in just three weighings. Firstly, split the 27 coins into three groups of 9 each and weigh any two groups. 

If they balance, the heavier coin resides within the remaining unweighted group of 9. If one of the groups tips the balance, it narrows the possibilities down to 9 coins. Proceed by dividing this group into three smaller sets of 3 coins each, and weigh two of these sets. 

If they balance, the heavier coin is in the remaining set of 3. Alternatively, if one set is heavier, the heavier coin within the 3 is now identified, having used only three weighings to reach a certain conclusion.

Solution of Two Stick Problem

To measure exactly 45 minutes using the two non-uniform burning sticks and a lighter, follow these steps:

1. Light one end of the first stick and both ends of the second stick simultaneously.
   
   
2. Simultaneously start a timer.
   
   
3. Once the second stick (which was lit at both ends) completely burns out, which should take 30 minutes since it burns twice as fast, 30 minutes will have passed.
   
   
4. At this point, there will be 30 minutes remaining on the first stick.
   
   
5. As soon as the second stick burns out, light one end of the first stick.
   
   
6. When the first stick (which was relit) completely burns out, which will take 15 more minutes, a total of 45 minutes will have passed.

By using these two sticks and the described method, you can accurately measure 45 minutes.

That's all on this list of top 10 puzzles, riddles, logical questions, and lateral thinking questions asked in programmer interviews. These questions have maximum impact when the programmer doesn't hear about them, and it means they may appear differently in the actual interview. 

As a candidate, you can prepare all these questions to get your mind working and knowing some techniques to solve them but be prepared for surprise in the actual Interview. The key of solving puzzles, logical questions, or riddles is keeping your cool and not panicking.

Even if you don't know the answer you should start explaining your way and logic and if you have any answer which is out of the box then better say it. Many times it happens when candidates are selected even if they don't solve the puzzles but in the process show some promise.