fun main() { val builder = StringBuilder() val mod = 1000000007L // 解説読むとなんでこんな単純な数え上げもできないのかと嫌になりますね val n = readInputLine().toInt() val edges = Array(n) { mutableListOf() } repeat(n - 1) { val (u, v) = readInputLine().split(" ").map { it.toInt() - 1 } edges[u].add(v) edges[v].add(u) } // 1~nの階乗、逆元 val factorial = LongArray(n + 1) val inverse = LongArray(n + 1) val factorialInverse = LongArray(n + 1) factorial[0] = 1L factorial[1] = 1L inverse[0] = 1L inverse[1] = 1L factorialInverse[0] = 1L factorialInverse[1] = 1L for (i in 2..n) { factorial[i] = (factorial[i - 1] * i.toLong() % mod) inverse[i] = (mod - inverse[mod.toInt() % i] * (mod / i.toLong()) % mod) factorialInverse[i] = (factorialInverse[i - 1] * inverse[i] % mod) } fun nCm(n: Int, m: Int): Long { return factorial[n] * (factorialInverse[m] * factorialInverse[n - m] % mod) % mod } fun dfs(node: Int, parent: Int, depth: Int): Long { var ret = nCm(n, depth) * factorial[depth - 1] % mod * factorial[n - depth] for (e in edges[node]) { if (e == parent) { continue } ret += dfs(e, node, depth + 1) ret %= mod } return ret } builder.appendln(dfs(0, -1, 1)) print(builder.toString()) } fun readInputLine(): String { return readLine()!! }