花花酱 LeetCode 676. Implement Magic Dictionary

zxi — Sun, 10 Sep 2017 21:00:40 +0000

Problem:

Implement a magic directory with buildDict, and search methods.

For the method buildDict, you’ll be given a list of non-repetitive words to build a dictionary.

For the method search, you’ll be given a word, and judge whether if you modify exactly one character into another character in this word, the modified word is in the dictionary you just built.

Example 1:

Input: buildDict(["hello", "leetcode"]), Output: Null
Input: search("hello"), Output: False
Input: search("hhllo"), Output: True
Input: search("hell"), Output: False
Input: search("leetcoded"), Output: False

Note:

You may assume that all the inputs are consist of lowercase letters a-z.
For contest purpose, the test data is rather small by now. You could think about highly efficient algorithm after the contest.
Please remember to RESET your class variables declared in class MagicDictionary, as static/class variables are persisted across multiple test cases. Please see here for more details.

Idea:

Fuzzy match

Time Complexity:

buildDict: O(n*m)

n: numbers of words

m: length of word

search: O(m)

m: length of word

Space Complexity:

O(n*m)

Solution:

// Author: Huahua
class MagicDictionary {
public:
    /** Initialize your data structure here. */
    MagicDictionary() {
        dict_.clear();
    }
    
    /** Build a dictionary through a list of words */
    void buildDict(vector dict) {
        for(string& word: dict) {
            for(int i = 0; i < word.length(); ++i) {
                char c = word[i];
                word[i] = '*';
                dict_[word].insert(c);
                word[i] = c;
            }
        }
    }
    
    /** Returns if there is any word in the trie that equals to the given word after modifying exactly one character */
    bool search(string word) {
        for(int i = 0; i < word.length(); ++i) {
            char c = word[i];
            word[i] = '*';
            if (dict_.count(word)) {
                const auto& char_set = dict_[word];
                if (!char_set.count(c) || char_set.size() > 1)
                    return true;
            }
            word[i] = c;
        }
        return false;
    }
private:
    unordered_map> dict_;
};

/**
 * Your MagicDictionary object will be instantiated and called as such:
 * MagicDictionary obj = new MagicDictionary();
 * obj.buildDict(dict);
 * bool param_2 = obj.search(word);
 */

Java / Trie

class MagicDictionary {
    private Trie root;    
    
    public MagicDictionary() {
        root = new Trie();
    } 
    
    public void buildDict(String[] dict) {
        for (String word : dict) {
            Trie curr = root;
            for (char c : word.toCharArray()) {                
                int index = c - 'a';
                if (curr.children[index] == null)
                    curr.children[index] = new Trie();
                curr = curr.children[index];
            }
            curr.ends = true;
        }
    }  
    
    public boolean search(String word) {
        char[] s = word.toCharArray();
        for(int i = 0; i < s.length; i++) {
            for (char c = 'a'; c <= 'z'; ++c) {
                if (s[i] == c) continue;
                char tmp = s[i];
                s[i] = c;
                if (contains(s)) return true;
                s[i] = tmp;
            }
        }
        return false;
    }
    
    private boolean contains(char[] word) {        
        Trie curr = root;
        for (int i = 0; i < word.length; ++i) {
            curr = curr.children[word[i] - 'a'];
            if (curr == null) return false;            
        }
        return curr.ends;
    }
    
    class Trie {
        private boolean ends;
        private Trie[] children;
        public Trie() {
            children = new Trie[26];
            ends = false;
        }
    }
}

Java / Trie v2

class MagicDictionary {
    private Trie root;    
    
    public MagicDictionary() {
        root = new Trie();
    } 
    
    public void buildDict(String[] dict) {
        for (String word : dict) {
            Trie curr = root;
            for (char c : word.toCharArray()) {                
                int index = c - 'a';
                if (curr.children[index] == null)
                    curr.children[index] = new Trie();
                curr = curr.children[index];
            }
            curr.ends = true;
        }
    }  
    
    public boolean search(String word) {
        char[] s = word.toCharArray();
        Trie prefix = root;
        for(int i = 0; i < s.length; i++) {
            for (char c = 'a'; c <= 'z'; ++c) {
                if (s[i] == c) continue;
                char tmp = s[i];
                s[i] = c;
                if (contains(s, prefix, i)) return true;
                s[i] = tmp;                
            }
            prefix = prefix.children[s[i] - 'a'];
            if (prefix == null) return false;
        }
        return false;
    }
    
    private boolean contains(char[] word, Trie prefix, int s) {        
        Trie curr = prefix;
        for (int i = s; i < word.length; ++i) {
            curr = curr.children[word[i] - 'a'];
            if (curr == null) return false;
        }
        return curr.ends;
    }
    
    class Trie {
        private boolean ends;
        private Trie[] children;
        public Trie() {
            children = new Trie[26];
            ends = false;
        }
    }
}

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花花酱 LeetCode 676. Implement Magic Dictionary