Longest Word in Dictionary

Longest Word in Dictionary

Given a list of strings words representing an English Dictionary, find the longest word in words that can be built one character at a time by other words in words. If there is more than one possible answer, return the longest word with the smallest lexicographical order. If there is no answer, return the empty string.

Example 1:

Input: 
words = ["w","wo","wor","worl", "world"]
Output: "world"
Explanation: 
The word "world" can be built one character at a time by "w", "wo", "wor", and "worl".

Example 2:

Input: 
words = ["a", "banana", "app", "appl", "ap", "apply", "apple"]
Output: "apple"
Explanation: 
Both "apply" and "apple" can be built from other words in the dictionary. However, "apple" is lexicographically smaller than "apply".

Note:All the strings in the input will only contain lowercase letters.The length of words will be in the range [1, 1000].The length of words[i] will be in the range [1, 30].

Solutions

🧠 Cpp

#define all(x) begin(x),end(x)

class Solution
{

    struct TrieNode
    {
        char value = ' ';
        bool is_wordend = false;
        vector<shared_ptr<TrieNode>> nodes;
    };

    shared_ptr<TrieNode> createTrie(const vector<string>& words)
    {
        auto root = make_shared<TrieNode>();

        //translate vector of strings into trie
        for(const auto &str : words)
        {
            //start inserting new word from trie root
            auto trie_pointer = root;
            for(auto ch_iter = begin(str); ch_iter < end(str); ++ch_iter)
            {
                const char ch = *ch_iter;
                const bool char_present_in_trie = std::any_of(all(trie_pointer->nodes),
                    [&trie_pointer, ch](auto node)
                    {
                      bool found = node->value == ch;
                      if (found)
                          trie_pointer = node;
                        return found;
                    });

                //insert new node
                if(!char_present_in_trie)
                {
                    auto node = make_shared<TrieNode>();
                    node->value = ch;
                    trie_pointer->nodes.push_back(node);
                    trie_pointer = node;
                }

                if(ch_iter == prev(end(str)))
                    trie_pointer->is_wordend = true;
            }
        }

        return root;
    }
public:

    vector<string> get_words_formed_by_words(const shared_ptr<TrieNode> root)
    {
        vector<string> res;

        for(auto &leaf : root->nodes)
        {
            if(leaf->is_wordend)
            {
                res.emplace_back(1, leaf->value);

                vector<string> subres = get_words_formed_by_words(leaf);
                if(!subres.empty())
                {
                    string last_letter = res.back();
                    for(auto &str : subres)
                    res.push_back(last_letter + str);
                }
            }
        }

        return res;
    }

    string longestWord(vector<string>& words)
    {
        //O(n)
        auto root = createTrie(words);

        //O(n)
        vector<string> wfbw = get_words_formed_by_words(root);

        //O(n)
        return *max_element(all(wfbw), 
                            [](auto a, auto b)
                            {
                                return a.size() == b.size() ?
                                       a > b :
                                       a.size() <  b.size();
                            });
    }
};