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a.go
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a.go
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package main
// github.com/EndlessCheng/codeforces-go
const mod int = 1e9 + 7
type matrix [][]int
func newMatrix(n, m int) matrix {
a := make(matrix, n)
for i := range a {
a[i] = make([]int, m)
}
return a
}
func newMatrixI(n int) matrix {
a := make(matrix, n)
for i := range a {
a[i] = make([]int, n)
a[i][i] = 1
}
return a
}
func (a matrix) mul(b matrix) matrix {
c := newMatrix(len(a), len(b[0]))
for i, row := range a {
for j := range b[0] {
for k, aik := range row {
c[i][j] += aik * b[k][j] % mod
}
c[i][j] %= mod
}
}
return c
}
func (a matrix) pow(k int) matrix {
res := newMatrixI(len(a))
for ; k > 0; k >>= 1 {
if k&1 == 1 {
res = res.mul(a)
}
a = a.mul(a)
}
return res
}
func calcFibonacci(p, q, a0, a1, n int) int {
if n == 0 {
return a0
}
if n == 1 {
return a1
}
m := matrix{{p, q}, {1, 0}}.pow(n - 1)
return (m[0][0]*a1 + m[0][1]*a0) % mod
}
func Answerforcn(N int64) int {
n := int(N) - 1
a := calcFibonacci(2, 3, 2, 6, n)
b := calcFibonacci(3, 10, 7, 35, n)
return a * b % mod
}