Create 2466-count-ways-to-build-good-strings.kt

Author: a93a

kotlin/2466-count-ways-to-build-good-strings.kt

@@ -0,0 +1,45 @@
+/*
+* Recursion/DFS + memoization
+*/
+class Solution {
+    fun countGoodStrings(low: Int, high: Int, zero: Int, one: Int): Int {
+        val dp = IntArray(high + 1) { -1 }
+        val mod = 1000000007
+
+        fun dfs(i: Int): Int {
+            if (i > high) 
+                return 0
+            if (dp[i] != -1)
+                return dp[i]
+            
+            dp[i] = if (i >= low) 1 else 0
+            dp[i] += dfs(i + zero) + dfs(i + one)
+            dp[i] = dp[i] % mod
+
+            return dp[i]
+        }
+
+        return dfs(0)
+    }
+}
+
+/*
+* Bottom up DP
+*/
+class Solution {
+    fun countGoodStrings(low: Int, high: Int, zero: Int, one: Int): Int {
+        val dp = IntArray(high + 1)
+        val mod = 1000000007
+
+        dp[0] = 1
+        for (i in 1..high) {
+            dp[i] += if (i - one >= 0) dp[i - one] else 0
+            dp[i] += if (i - zero >= 0) dp[i - zero] else 0
+            dp[i] = dp[i] % mod
+        }
+
+        var sum = 0
+        for (i in low..high) sum = (sum + dp[i]) % mod
+        return sum
+    }
+}