implement-magic-dictionary.cpp

// Time:  O(n), n is the length of the word
// Space: O(d)

class MagicDictionary {
public:
    /** Initialize your data structure here. */
    MagicDictionary() {
        
    }
    
    /** Build a dictionary through a list of words */
    void buildDict(vector<string> dict) {
        string result;
        for (const auto& s : dict) {
            trie_.Insert(s);
        }
    }
    
    /** Returns if there is any word in the trie that equals to the given word after modifying exactly one character */
    bool search(string word) {
        return find(word, &trie_, 0, true);    
    }

private:
    struct TrieNode {
        bool isString = false;
        unordered_map<char, TrieNode *> leaves;
        
        void Insert(const string& s) {
            auto* p = this;
            for (const auto& c : s) {
                if (p->leaves.find(c) == p->leaves.cend()) {
                    p->leaves[c] = new TrieNode;
                }
                p = p->leaves[c];
            }
            p->isString = true;
        }
        
        ~TrieNode() {
            for (auto& kv : leaves) {
                if (kv.second) {
                    delete kv.second;
                }
            }
        }
    };

    bool find(const string& word, TrieNode *curr, int i, bool mistakeAllowed) {
        if (i == word.length()) {
            return curr->isString && !mistakeAllowed; 
        }

        if (!curr->leaves.count(word[i])) {
            return mistakeAllowed ?
                       any_of(curr->leaves.begin(), curr->leaves.end(),
                              [&](const pair<char, TrieNode *>& kvp) { 
                                  return find(word, kvp.second, i + 1, false);
                               }) :
                       false;
        }
                    
        if (mistakeAllowed) {
            return find(word, curr->leaves[word[i]], i + 1, true) ||
                   any_of(curr->leaves.begin(), curr->leaves.end(),
                          [&](const pair<char, TrieNode *>& kvp) { 
                              return kvp.first != word[i] && find(word, kvp.second, i + 1, false);
                          });
        }
        return find(word, curr->leaves[word[i]], i + 1, false);
    }

    TrieNode trie_;
};

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