word dictionary

Author: zgpeace

code/LeetCode/src/backtracking/WordDictionary.java

@@ -0,0 +1,100 @@
+package backtracking;
+
+// https://leetcode.com/problems/add-and-search-word-data-structure-design/
+
+import java.util.HashMap;
+import java.util.HashSet;
+import java.util.Map;
+import java.util.Set;
+
+/**
+ * Your WordDictionary object will be instantiated and called as such:
+ * WordDictionary obj = new WordDictionary();
+ * obj.addWord(word);
+ * boolean param_2 = obj.search(word);
+ */
+public class WordDictionary {
+
+  private class TrieNode {
+    private boolean isWord;
+    private Map<Character, TrieNode> childMap;
+
+    public TrieNode() {
+      isWord = false;
+      childMap = new HashMap<Character, TrieNode>();
+    }
+
+  }
+
+  private TrieNode root;
+
+  /** Initialize your data structure here. */
+  public WordDictionary() {
+    root = new TrieNode();
+  }
+
+  /** Adds a word into the data structure. */
+  public void addWord(String word) {
+    TrieNode curr = root;
+    for (char c: word.toCharArray()) {
+      if (!curr.childMap.containsKey(c)) {
+        curr.childMap.put(c, new TrieNode());
+      }
+      curr = curr.childMap.get(c);
+    }
+
+    curr.isWord = true;
+  }
+
+  /** Returns if the word is in the data structure. A word could contain the dot character '.' to represent any one letter. */
+  public boolean search(String word) {
+    return dfs(word,0, root);
+  }
+
+  public boolean dfs(String word, int pos, TrieNode node) {
+    // if the word has all been scanned, return
+    if (pos == word.length()) {
+      return node.isWord;
+    }
+    // reach the leaf before finishing scanning the word
+    if (node.childMap.size() == 0) {
+      return false;
+    }
+
+    Character c = word.charAt(pos);
+    // if the character at current position is '.',
+    // recursive check whether the remaining word is in the trie
+    if (c == '.') {
+      for (char item: node.childMap.keySet()) {
+        if (dfs(word, pos + 1, node.childMap.get(item))) {
+          return true;
+        }
+      }
+    }
+
+    // if character at position 'pos' is neither equal to the node nor '.', return false
+    if (!node.childMap.containsKey(c)) {
+      return false;
+    }
+
+    // if character at current position matches the node,
+    // recursively search the remaining word
+    return dfs(word, pos + 1, node.childMap.get(c));
+  }
+
+  public static void main(String[] args) {
+    WordDictionary obj = new WordDictionary();
+    obj.addWord("bad");
+    obj.addWord("dad");
+    obj.addWord("mad");
+    obj.addWord("a");
+    System.out.println(obj.search("pad"));
+    System.out.println(obj.search("bad"));
+    System.out.println(obj.search(".ad"));
+    System.out.println(obj.search("b.."));
+    //obj.search("pad") -> false
+    //obj.search("bad") -> true
+    //obj.search(".ad") -> true
+    //obj.search("b..") -> true
+  }
+}