14 lines
215 B
Go
14 lines
215 B
Go
package main
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const MOD int = 1_000_000_007
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func numTilings(n int) int {
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dp := [...]int{0, 1, 2, 5}
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for n >= 4 {
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dp[0], dp[1], dp[2], dp[3] = dp[1], dp[2], dp[3], (2*dp[3]+dp[1])%MOD
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n--
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}
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return dp[n]
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}
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