complete 11057.kt 15835.kt 20411.kt 25345.kt 28242.kt 32628.kt

storage/zeta/kt/completed/25345.kt

@@ -0,0 +1,56 @@
+const val MOD = 1_000_000_007
+
+val MEM_CHOOSE = Array<LongArray>(2001) { LongArray(2000) { -1 } }
+val MEM_POW = LongArray(2001) { -1 }
+
+fun choose(n: Int, k: Int): Long {
+    if (MEM_CHOOSE[n][k] != -1L) {
+        return MEM_CHOOSE[n][k]
+    }
+    if (n == 1 || n == 0) {
+        MEM_CHOOSE[n][k] == 1L
+        return 1
+    } else if (k == 0) {
+        MEM_CHOOSE[n][k] = 1
+        return 1
+    } else if (k == 1) {
+        MEM_CHOOSE[n][k] = n.toLong()
+        return n.toLong()
+    } else if (k == n) {
+        MEM_CHOOSE[n][k] = 1
+        return 1
+    } else if (k == n - 1) {
+        MEM_CHOOSE[n][k] = n.toLong()
+        return n.toLong()
+    } else {
+        val res = (choose(n - 1, k - 1) + choose(n - 1, k)) % MOD
+        MEM_CHOOSE[n][k] = res
+        return res
+    }
+}
+
+
+fun powOf2(n: Int): Long {
+    if (MEM_POW[n] != -1L) {
+        return MEM_POW[n]
+    }
+    if (n == 0) {
+        MEM_POW[n] = 1L
+        return 1
+    } else {
+        val res = (powOf2(n - 1) * 2) % MOD
+        MEM_POW[n] = res
+        return res
+    }
+}
+
+fun modifier(k: Int): Long {
+    return powOf2(k - 1)
+}
+
+
+fun main() = with(System.`in`.bufferedReader()) {
+    val (n, k) = this.readLine().split(" ").map { it.toInt() }
+    // val arr = this.readLine().split(" ").map { it.toInt() }
+    println(choose(n, k) * modifier(k) % MOD)
+}