From 3037205bba2852e7a824f7679b439aab95289dbc Mon Sep 17 00:00:00 2001
From: Manuel Pineda <manuelpineda@google.com>
Date: Sun, 17 Jan 2021 13:01:21 +0100
Subject: [PATCH] [LeetCode] Add January 17.

---
 solved/LeetCode/Challenges/2020/January/17.kt | 25 +++++++++++++++++++
 1 file changed, 25 insertions(+)
 create mode 100644 solved/LeetCode/Challenges/2020/January/17.kt

diff --git a/solved/LeetCode/Challenges/2020/January/17.kt b/solved/LeetCode/Challenges/2020/January/17.kt
new file mode 100644
index 00000000..d4361f5f
--- /dev/null
+++ b/solved/LeetCode/Challenges/2020/January/17.kt
@@ -0,0 +1,25 @@
+class Solution {
+  data class State(val n: Int, val last: Int)
+  val seen = mutableMapOf<State, Int>()
+  
+  fun countVowelStrings(n: Int): Int {
+    return count(State(n, 0))
+  }
+  
+  private fun count(s: State) : Int {
+    if (s.n == 0) {
+      return 1
+    }
+    
+    if (seen.contains(s)) {
+      return seen[s]!!
+    }
+    
+    var ans = 0
+    for (next in s.last..4) {
+      ans += count(State(s.n-1, next))
+    }
+    seen[s] = ans
+    return ans
+  }
+}