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

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

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+/*
+* 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
+ }
+}