liars-and-truth-tellers

A brute-force solver for problems about truth tellers and liars

How to use

Below the # Your code goes below! comment, you should describe the problem. You can check if two people act the same (that is, if they are both truth tellers or both liars) using the equality operator ==, or if they are different using the inequality operator !=. You can check if they are a truth teller using the .isTruthTeller() method, and if they are a liar using the .isLiar() method.

You can supply an array of many conditions, and if you want to quote what somebody has said you can use the person.said() method.

All the people involved are supplied in an array.

Example

In these examples, we only have one condition. If multiple people in the world of truth tellers and liars are speaking, you will want to pass more functions into the array of functions.

I am a liar!

⚠️ Spoiler alert, the following examples contain answers to some truth-tellers-and-liars puzzles. Instead of reading on, I suggest you have a go at solving them.

Let's say you have one person, let's call them A, that says I'm a liar!, and you want to check if this is actually possible in a world where people either always lie, or always tell the truth.

First, you need to describe the problem. We need to use the .said() method to quote A, and we need to describe what A said using .isLiar().

The first argument is the amount of people we want. In this case, we only want one person, A.

print(calc(1, # Number of people 
  [
    lambda people: 
      people[0].said( # A said that
        people[0].isLiar() # A is a liar
      )
  ]
))

And that will output

[]

because it is impossible to say you are a liar. If you are a liar, then when you say I am a liar!, you are actually lying about that. But that means you are a truth-teller. Contradiction!

If you are a truth-teller, then you are directly saying you are a liar. Again, contradiction!

Between my brother and I, at least one of us is a liar!

Let's call the speaker A, and the brother B. We will want to use .said() to quote what A said, and then we will have to explain what A did say.

We need two people. Let's write code! :D

print(calc(2, # Number of people
  [
    lambda people: people[0].said( # A said
      people[0].isLiar() or # Either A is a liar, or 
      people[1].isLiar()    # B is a liar
    )
  ]
))

This will output

['10']

That means there is only one combination that will fit the criteria supplied. This combination is 10. 1 means truth teller, and 0 means liar, so 10 means A is a truth teller, and B is a liar.

Does this solution work? Well, yes, and in fact, it is the only solution.

Ending remarks