Create 1220-count-vowels-permutation.kt

Author: a93a

kotlin/1220-count-vowels-permutation.kt

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+//DP
+class Solution {
+    fun countVowelPermutation(n: Int): Int {
+        val mod = 1_000_000_000 + 7
+        val dp = Array (n + 1) { LongArray (5) }
+        
+        for (j in 0 until 5) 
+            dp[1][j] = 1
+
+        val a = 0
+        val e = 1
+        val i = 2
+        val o = 3
+        val u = 4
+
+        for (j in 2..n) {
+            dp[j][a] = 0L + (dp[j - 1][e] + dp[j - 1][i] + dp[j - 1][u]) % mod
+            dp[j][e] = 0L + (dp[j - 1][a] + dp[j - 1][i]) % mod
+            dp[j][i] = 0L + (dp[j - 1][e] + dp[j - 1][o]) % mod
+            dp[j][o] = 0L + (dp[j - 1][i]) % mod
+            dp[j][u] = 0L + (dp[j - 1][i] + dp[j - 1][o]) % mod
+        }
+
+        return (dp[n].sum()!! % mod).toInt()
+    }
+}
+
+//recursion + memoization
+class Solution {
+    fun countVowelPermutation(n: Int): Int {
+        val mod = 1_000_000_000 + 7
+        val dp = Array (n) { IntArray (5) { -1 } }
+
+        val a = 0
+        val e = 1
+        val i = 2
+        val o = 3
+        val u = 4
+
+        val follow = mapOf(
+            a to listOf(e),
+            e to listOf(a, i),
+            i to listOf(a, e, o, u),
+            o to listOf(i, u),
+            u to listOf(a)
+        )
+
+        fun dfs(idx: Int, prev: Int): Int {
+            if (idx == n) return 1
+            if (dp[idx][prev] != -1) return dp[idx][prev]
+        
+            var res = 0
+            follow[prev]?.forEach {
+                res = (res + dfs(idx + 1, it)) % mod
+            }
+
+            dp[idx][prev] = res
+            return res
+        }
+
+        var res = 0
+        follow.keys.forEach {
+            res = (res + dfs(1, it)) % mod
+        }
+
+        return res
+    }
+}