feat: word-search-ii

Author: minji-go

word-search-ii/minji-go.java

@@ -0,0 +1,73 @@
+/**
+ * <a href="https://leetcode.com/problems/word-search-ii/">week14-5. word-search-ii</a>
+ * <li>Description: Given an m x n board of characters and a list of strings words, return all words on the board.</li>
+ * <li>Topics: Array, String, Backtracking, Trie, Matrix</li>
+ * <li>Time Complexity: O(M*N*4^L), Runtime 446ms   </li>
+ * <li>Space Complexity: O(K*L), Memory 44.81MB</li>
+ * <li>Note: Refer to answer </li>
+ */
+class Solution {
+
+    class TrieNode {
+        Map<Character, TrieNode> children = new HashMap<>();
+        String word = null;
+    }
+
+    public List<String> findWords(char[][] board, String[] words) {
+        TrieNode root = buildTrie(words);
+        List<String> result = new ArrayList<>();
+
+        for (int i = 0; i < board.length; i++) {
+            for (int j = 0; j < board[0].length; j++) {
+                if (root.children.containsKey(board[i][j])) {
+                    TrieNode node = root.children.get(board[i][j]);
+                    findWord(board, i, j, node, result);
+                }
+            }
+        }
+
+        return result;
+    }
+
+    private TrieNode buildTrie(String[] words) {
+        TrieNode root = new TrieNode();
+
+        for (String word : words) {
+            TrieNode node = root;
+            for (char c : word.toCharArray()) {
+                node = node.children.computeIfAbsent(c, k -> new TrieNode());
+            }
+            node.word = word;
+        }
+        return root;
+    }
+
+    private int[][] directions = {{-1, 0}, {1, 0}, {0, -1}, {0, 1}};
+
+    private void findWord(char[][] board, int r, int c, TrieNode node, List<String> result) {
+        if (node.word != null) {
+            result.add(node.word);
+            node.word = null;
+        }
+
+        char letter = board[r][c];
+        board[r][c] = '#';
+
+        for (int[] direction : directions) {
+            int nr = r + direction[0];
+            int nc = c + direction[1];
+
+            if (nr < 0 || nr > board.length - 1 || nc < 0 || nc > board[0].length - 1) {
+                continue;
+            }
+            if (node.children.containsKey(board[nr][nc])) {
+                TrieNode nextNode = node.children.get(board[nr][nc]);
+                findWord(board, nr, nc, nextNode, result);
+            }
+        }
+
+        board[r][c] = letter;
+    }
+
+}
+