Create 1639-number-of-ways-to-form-a-target-string-given-a-dictionary.kt

Author: a93a

Diff for: kotlin/1639-number-of-ways-to-form-a-target-string-given-a-dictionary.kt

@@ -0,0 +1,34 @@
+class Solution {
+    fun numWays(words: Array<String>, target: String): Int {
+        val mod = 1000000000 + 7
+        val m = words[0].length
+        val n = target.length
+        
+        val count = Array(m){IntArray(26)}
+        for (w in words) {
+            for ((i, c) in w.withIndex()) {
+                count[i][c - 'a'] += 1
+            }
+        }
+        
+        val dp = Array(n){LongArray(m){-1L}}
+
+        fun dfs(i: Int, k: Int): Long {
+            if (i == n)
+                return 1L
+            if (k == m)
+                return 0L
+            if (dp[i][k] != -1L)
+                return dp[i][k]
+
+            val c = target[i]
+            dp[i][k] = dfs(i, k + 1)
+            if(count[k][c - 'a'] != 0)
+                dp[i][k] += count[k][c - 'a'] * dfs(i + 1, k + 1)
+
+            return dp[i][k] % mod
+        }
+
+        return dfs(0, 0).toInt()
+    }
+}