package main import ( "bufio" "fmt" "math" "os" ) func main() { // https://yukicoder.me/problems/no/1339 // 求有理数1/n的循环节长度 in := bufio.NewReader(os.Stdin) out := bufio.NewWriter(os.Stdout) defer out.Flush() var T int fmt.Fscan(in, &T) for t := 0; t < T; t++ { var n int fmt.Fscan(in, &n) // 让模与10互质 for n%2 == 0 { n /= 2 } for n%5 == 0 { n /= 5 } if n == 1 { fmt.Fprintln(out, 1) continue } // !求解 10^k mod n = 1 的最小整数解 k, 其中 1<=k<=n+1 k := DiscreteLogGroup( func() G { return 1 % n }, func(g1, g2 G) G { return g1 * g2 % n }, func(g G) G { return modInv(g, n) }, 10, 1, 1, n+10, ) fmt.Fprintln(out, k) } } type G = int // 给定一个群G,群元素a, b in G,求解 a^n = b 的最小非负整数解 n. // 返回在[lower, higher)中的第一个解,如果不存在则返回-1. // !可以理解为 a 经过多少次群运算后可以到达 b. func DiscreteLogGroup( /** 群G */ e func() G, op func(g1, g2 G) G, inv func(g G) G, a G, b G, lower, higher int, ) int { aInv := inv(a) UNIT := e() if op(a, aInv) != UNIT { panic("a is not invertible") } if lower >= higher { return -1 } s := UNIT mp := make(map[G]int) aPow := func(n int) G { p := a res := UNIT for n > 0 { if n&1 == 1 { res = op(res, p) } p = op(p, p) n /= 2 } return res } s = op(s, aPow(lower)) LIM := higher - lower K := int(math.Sqrt(float64(LIM))) + 1 for i := 0; i <= K; i++ { key := s if _, ok := mp[key]; !ok { mp[key] = i } if i != K { s = op(s, a) } } a = inv(aPow(K)) for i := 0; i <= K; i++ { key := b if v, ok := mp[key]; ok { res := i*K + v + lower if res >= higher { return -1 } return res } b = op(b, a) } return -1 } func exgcd(a, b int) (gcd, x, y int) { if b == 0 { return a, 1, 0 } gcd, y, x = exgcd(b, a%b) y -= a / b * x return } func modInv(a, mod int) int { gcd, x, _ := exgcd(a, mod) if gcd != 1 { panic(fmt.Sprintf("no inverse element for %d", a)) } return (x%mod + mod) % mod } // 求离散对数 a^n = b (mod m) 的最小非负整数解 n. // 其中模数为质数. // 如果不存在则返回-1. func ModLog(a, b, mod int) int { a %= mod b %= mod p := 1 % mod for k := 0; k < 32; k++ { if p == b { return k } p = p * a % mod } if a == 0 || b == 0 { return -1 } gcd := func(a, b int) int { for b != 0 { a, b = b, a%b } return a } g := gcd(mod, p) if b%g != 0 { return -1 } mod /= g a %= mod b %= mod if gcd(b, mod) > 1 { return -1 } return DiscreteLogGroup( func() G { return 1 % mod }, func(g1, g2 G) G { return (g1 * g2) % mod }, func(g G) G { return modInv(g, mod) }, a, b, 32, mod, ) } func testModLog() { // https://www.luogu.com.cn/problem/P4195 in := bufio.NewReader(os.Stdin) out := bufio.NewWriter(os.Stdout) defer out.Flush() for { var base, p, target int _, _ = fmt.Fscan(in, &base, &p, &target) if base == target && target == p && p == 0 { break } res := ModLog(base, target, p) if res == -1 { fmt.Fprintln(out, "No Solution") } else { fmt.Fprintln(out, res) } } }