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12 lines
405 B
Kotlin
12 lines
405 B
Kotlin
// How to get k-th odd number: p = 2k + 1 (zero indexed)
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// Decomposition:
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// 1. Find out how many odd numbers we have in front
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// 2. Figure out next index
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// 3. Sum those numbers
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private fun kthOdd(k: Int): Int = 2*k + 1
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private fun oddNumbersBefore(n: Int) = n.times(n + 1).div(2)
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fun rowSumOddNumbers(n: Int): Int =
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(oddNumbersBefore(n - 1)..oddNumbersBefore(n) - 1)
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.sumOf { kthOdd(it) }
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