Debugging Solutions

Some puzzles are tricky, you are so close to the right solution but there's a pesky bug hiding in plain sight.

To hunt for it, it's better to make use of the debugger than to spam your code with .also(::println)!

However, there's a problem. If you run the whole AdventSpec in debug mode, you might not trigger the breakpoint when you expect, because the solution is run against multiple inputs and examples.

To fix this, you can define isolated runs.

Debug Scope

In your AdventSpec, you can use the debug scope, which will provide the instance of the solution, as well as your puzzle input, if it is available. When this scope is used, it defines a focused test, meaning any other parts and examples will be ignored and won't run.

You can then use the AdventSpec gutter icon to run the test in debug mode.

@AdventDay(9999, 1, "Magic Numbers")
class Y9999D01 : AdventSpec<Y9999D01>({
    
    debug {
        solution.partOne("<handcrafted input or edge case>")
        // or, to run on your actual input
        solution.partOne(input)
    }
    
    // Any other declarations are effectively ignored ...
})

Main Function

Alternatively, you can define a main function near your solution and call it manually. However, this method requires you to provide the input yourself.

IntelliJ will offer a gutter icon, right click it and run it with the debugger:

fun main() {
    Y9999D01.partOne("<handcrafted input or edge case>")  
} 

object Y9999D01 : Solution { /* ... */ }

19 November 2025