Create: 2707-extra-characters-in-a-string.kt

kotlin/2707-extra-characters-in-a-string.kt

@@ -0,0 +1,47 @@
+class Solution {
+
+    private lateinit var memo: IntArray
+
+    private class TrieNode {
+        val children = HashMap<Char, TrieNode>()
+        var isWord = false
+    }
+
+    fun minExtraChar(s: String, dictionary: Array<String>): Int {
+        val root = buildTrie(dictionary)
+        memo = IntArray(s.length) { -1 }
+        return dfs(0, s, root)
+    }
+
+    private fun dfs(index: Int, s: String, root: TrieNode): Int {
+        if (index == s.length) return 0
+        if (memo[index] != -1) return memo[index]
+
+        var result = 1 + dfs(index + 1, s, root)
+
+        var node = root
+        for (i in index until s.length) {
+            node = node.children[s[i]] ?: break
+            if (node.isWord) {
+                result = minOf(result, dfs(i + 1, s, root))
+            }
+        }
+
+        memo[index] = result
+        return result
+    }
+
+    private fun buildTrie(dictionary: Array<String>): TrieNode {
+        val root = TrieNode()
+
+        for (word in dictionary) {
+            var node = root
+            for (ch in word) {
+                node = node.children.getOrPut(ch) { TrieNode() }
+            }
+            node.isWord = true
+        }
+
+        return root
+    }
+}