Merge pull request neetcode-gh#766 from Raven1233/main

Added 211-Design-Add-And-Search-Words-Data-Structure.kt and 212-Words-Search-II.kt

Author: Ahmad-A0

kotlin/211-Design-Add-And-Search-Words-Data-Structure.kt

@@ -0,0 +1,25 @@
+class WordDictionary() {
+    data class TrieNode(var isLeaf: Boolean = false, val children: MutableMap<Char, TrieNode> = mutableMapOf())
+
+    val root = TrieNode()
+
+    fun addWord(word: String) {
+        var current = root
+        for (c in word) {
+            current = current.children.getOrPut(c) { TrieNode() }
+        }
+        current.isLeaf = true
+    }
+
+    fun search(word: String): Boolean {
+        var candidates = listOf(root)
+        for (c in word) {
+            candidates = when (c) {
+                '.' -> candidates.flatMap { it.children.values }
+                else -> candidates.mapNotNull { it.children[c] }
+            }
+            if (candidates.isEmpty()) return false
+        }
+        return candidates.any { it.isLeaf }
+    }
+}

kotlin/212-Word-Search-II.kt

@@ -0,0 +1,68 @@
+class Solution {
+    private companion object{
+        const val IMPOSSIBLE: Char = '#'
+        val DIRS = intArrayOf(0, -1, 0, 1, 0)
+    }
+
+    fun findWords(board: Array<CharArray>, words: Array<String>): List<String> {
+        val nRows = board.size
+        val nCols = board[0].size
+        val root = buildTrie(words)
+        val ans = mutableListOf<String>()
+        for(row in 0 until nRows){
+            for(col in 0 until nCols){
+                backtrack(row, col, board, root, ans)
+            }
+        }
+        return ans
+    }
+
+    private fun backtrack(row: Int, col: Int, board: Array<CharArray>, node: TrieNode, res: MutableList<String>){
+        val nRows = board.size
+        val nCols = board[0].size
+
+        if(row < 0 || row >= nRows || col < 0 || col >= nCols)
+            return
+
+        val hold = board[row][col]
+        val idx = hold.toInt() - 'a'.toInt();
+        if(hold == IMPOSSIBLE || node.children[idx] == null){
+            return
+        }
+
+        var cur: TrieNode? = node
+        cur = cur!!.children[idx]
+        if(cur!!.word != null){
+            res.add(cur.word!!)
+            cur.word = null
+        }
+
+        board[row][col] = IMPOSSIBLE
+        for(d in 0 until 4){
+            val r = row + DIRS[d]
+            val c = col + DIRS[d + 1]
+            backtrack(r, c, board, cur, res)
+        }
+        board[row][col] = hold
+    }
+
+    private fun buildTrie(words: Array<String>): TrieNode{
+        val root = TrieNode()
+        for(word in words){
+            var cur: TrieNode? = root
+            for(ch in word){
+                val idx = ch.toInt() - 'a'.toInt()
+                if(cur!!.children[idx] == null)
+                    cur.children[idx] = TrieNode()
+
+                cur = cur.children[idx]
+            }
+            cur!!.word = word
+        }
+        return root
+    }
+
+    private data class TrieNode(var word: String? = null){
+        val children: Array<TrieNode?> = Array(26){ null }
+    }
+}