44 lines
1.3 KiB
Kotlin
44 lines
1.3 KiB
Kotlin
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val MOD = 1000000007
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class Solution {
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private fun createState(): MutableList<MutableList<Int>> = (0..1).map { mutableListOf(0, 0, 0) }.toMutableList()
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fun checkRecord(n: Int): Int {
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val initialState = createState()
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initialState[0][0] = 1
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val finalState =
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(1..n).fold(initialState) { state, _ ->
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val nextState = createState()
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(0..1).flatMap { absences -> (0..2).map { lates -> absences to lates } }.forEach { (absences, lates) ->
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nextState[absences][0] = (nextState[absences][0] + state[absences][lates]) % MOD
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if (absences < 1) {
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nextState[absences + 1][0] = (nextState[absences + 1][0] + state[absences][lates]) % MOD
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}
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if (lates < 2) {
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nextState[absences][lates + 1] = (nextState[absences][lates + 1] + state[absences][lates]) % MOD
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}
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}
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return@fold nextState
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}
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return finalState.fold(0) { acc, it ->
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it.fold(acc) { acc, it ->
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(acc + it) % MOD
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}
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}
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}
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}
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fun main() {
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val s = Solution()
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check(s.checkRecord(2) == 8)
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check(s.checkRecord(1) == 3)
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check(s.checkRecord(10101) == 183236316)
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}
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