42 lines
1.1 KiB
Kotlin
42 lines
1.1 KiB
Kotlin
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package games.game2048
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/*
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* This function moves all the non-null elements to the beginning of the list
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* (by removing nulls) and merges equal elements.
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* The parameter 'merge' specifies the way how to merge equal elements:
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* it returns a new element that should be present in the resulting list
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* instead of two merged elements.
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*
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* If the function 'merge("a")' returns "aa",
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* then the function 'moveAndMergeEqual' transforms the input in the following way:
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* a, a, b -> aa, b
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* a, null -> a
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* b, null, a, a -> b, aa
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* a, a, null, a -> aa, a
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* a, null, a, a -> aa, a
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*
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* You can find more examples in 'TestGame2048Helper'.
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*/
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fun <T : Any> List<T?>.moveAndMergeEqual(merge: (T) -> T): List<T> {
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val mutableList = mutableListOf<T>()
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val oldList = filterNotNull()
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var index = 0
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while (true) {
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if (index >= oldList.size) break
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val first = oldList[index]
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val second = oldList.getOrNull(index + 1)
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if (first == second) {
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index += 2
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mutableList.add(merge(first))
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} else {
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index += 1
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mutableList.add(first)
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}
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}
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return mutableList
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}
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