Trie - 20181113

442. Implement Trie (Prefix Tree)

 class TrieNode {
     public boolean isWord;
     public TrieNode[] children;

     public TrieNode() {
         isWord = false;
         children = new TrieNode[26];
     }

 }

 public class Trie {
     private TrieNode root;

     public Trie() {
         // do intialization if necessary
         root = new TrieNode();
     }

     /*
      * @param word: a word
      * @return: nothing
      */
     public void insert(String word) {
         // write your code here
         if (word == null || word.length() == 0) {
             return;
         }
         TrieNode p = root;
         for (int i = 0; i < word.length(); i++) {
             int index = word.charAt(i) - 'a';
             if (p.children[index] == null) {
                 p.children[index] = new TrieNode();
             }
             p = p.children[index];
         }
         p.isWord = true;
     }

     public TrieNode find(String prefix) {
         if (prefix == null || prefix.length() == 0) {
             return null;
         }
         TrieNode p = root;
         for (int i = 0; i < prefix.length(); i++) {
             int index = prefix.charAt(i) - 'a';
             if (p.children[index] == null) {
                 return null;
             }
             p = p.children[index];
         }
         return p;
     }

     /*
      * @param word: A string
      * @return: if the word is in the trie.
      */
     public boolean search(String word) {
         // write your code here
         TrieNode p = find(word);
         return p != null && p.isWord;
     }

     /*
      * @param prefix: A string
      * @return: if there is any word in the trie that starts with the given prefix.
      */
     public boolean startsWith(String prefix) {
         // write your code here
         return find(prefix) != null;
     }
 }

473. Add and Search Word - Data structure design

 class TrieNode {
     public boolean isWord;
     public char c;
     public Map<Character, TrieNode> children;

     public TrieNode() {
         children = new HashMap<>();
     }

     public TrieNode(char c) {
         this.c = c;
         children = new HashMap<>();
     }
 }

 public class WordDictionary {
     /*
      * @param word: Adds a word into the data structure.
      * @return: nothing
      */
     TrieNode root = new TrieNode();

     public void addWord(String word) {
         // write your code here
         if (word == null || word.length() == 0) {
             return;
         }

         TrieNode p = root;
         for (int i = 0; i < word.length(); i++) {
             char c = word.charAt(i);
             if (p.children.get(c) == null) {
                 TrieNode child = new TrieNode();
                 p.children.put(c, child);
             }

             p = p.children.get(c);
         }
         p.isWord = true;
     }

     /*
      * @param word: A word could contain the dot character '.' to represent any one letter.
      * @return: if the word is in the data structure.
      */
     public boolean search(String word) {
         // write your code here
         if (word == null || word.length() == 0) {
             return false;
         }
         TrieNode p = root;

         for (int i = 0; i < word.length(); i++) {
             char c = word.charAt(i);
             if (c != '.') {
                 if (p.children.get(c) == null) {
                     return false;
                 }
                 p = p.children.get(c);
             } else {
                 for (Map.Entry<Character, TrieNode> entry : p.children.entrySet()) {
                     if (search(word.substring(0, i) + entry.getKey() + word.substring(i + 1, word.length()))) {
                         return true;
                     }
                 }
                 return false;
             }

         }

         return p.isWord;
     }
 }

132. Word Search II

 class TrieNode {
     String word;
     Map<Character, TrieNode> children;

     public TrieNode() {
         children = new HashMap<>();
     }
 }

 class TrieTree {
     TrieNode root;

     public TrieTree(TrieNode node) {
         this.root = node;
     }

     public void insert(String word) {
         if (word == null || word.length() == 0) {
             return;
         }
         TrieNode p = root;
         for (int i = 0; i < word.length(); i++) {
             char ch = word.charAt(i);
             if (!p.children.containsKey(ch)) {
                 p.children.put(ch, new TrieNode());
             }
             p = p.children.get(ch);
         }
         p.word = word;
     }
 }

 public class Solution {
     private int[] dx = {0, 1, 0, -1};
     private int[] dy = {1, 0, -1, 0};

     /**
      * @param board: A list of lists of character
      * @param words: A list of string
      * @return: A list of string
      */
     public List<String> wordSearchII(char[][] board, List<String> words) {
         // write your code here
         if (words == null || words.size() == 0) {
             return new ArrayList<>();
         }
         Set<String> res = new HashSet<>();
         TrieTree tree = new TrieTree(new TrieNode());
         for (String word : words) {
             tree.insert(word);
         }
         for (int i = 0; i < board.length; i++) {
             for (int j = 0; j < board[i].length; j++) {
                 dfs(board, i, j, res, tree.root);
             }
         }
         return new ArrayList<>(res);
     }

     public void dfs(char[][] board, int x, int y, Set<String> res, TrieNode node) {
         TrieNode child = node.children.get(board[x][y]);
         if (child == null) {
             return;
         }
         if (child.word != null) {
             if (!res.contains(child.word)) {
                 res.add(child.word);
             }
         }

         char tmp = board[x][y];
         board[x][y] = 0;
         for (int i = 0; i < dx.length; i++) {
             int nxtDx = x + dx[i];
             int nxtDy = y + dy[i];
             if (!isValid(board, nxtDx, nxtDy)) {
                 continue;
             }
             dfs(board, nxtDx, nxtDy, res, child);
         }
         board[x][y] = tmp;
     }

     public boolean isValid(char[][] board, int x, int y) {
         if (x < 0 || x >= board.length || y < 0 || y >= board[0].length) {
             return false;
         }
         return board[x][y] != 0;
     }
 }