<p>Given an array of strings <code>words</code> representing an English Dictionary, return <em>the longest word in</em> <code>words</code> <em>that can be built one character at a time by other words in</em> <code>words</code>.</p>

<p>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.</p>

<p>Note that the word should be built from left to right with each additional character being added to the end of a previous word.&nbsp;</p>

<p>&nbsp;</p>
<p><strong class="example">Example 1:</strong></p>

<pre>
<strong>Input:</strong> words = [&quot;w&quot;,&quot;wo&quot;,&quot;wor&quot;,&quot;worl&quot;,&quot;world&quot;]
<strong>Output:</strong> &quot;world&quot;
<strong>Explanation:</strong> The word &quot;world&quot; can be built one character at a time by &quot;w&quot;, &quot;wo&quot;, &quot;wor&quot;, and &quot;worl&quot;.
</pre>

<p><strong class="example">Example 2:</strong></p>

<pre>
<strong>Input:</strong> words = [&quot;a&quot;,&quot;banana&quot;,&quot;app&quot;,&quot;appl&quot;,&quot;ap&quot;,&quot;apply&quot;,&quot;apple&quot;]
<strong>Output:</strong> &quot;apple&quot;
<strong>Explanation:</strong> Both &quot;apply&quot; and &quot;apple&quot; can be built from other words in the dictionary. However, &quot;apple&quot; is lexicographically smaller than &quot;apply&quot;.
</pre>

<p>&nbsp;</p>
<p><strong>Constraints:</strong></p>

<ul>
	<li><code>1 &lt;= words.length &lt;= 1000</code></li>
	<li><code>1 &lt;= words[i].length &lt;= 30</code></li>
	<li><code>words[i]</code> consists of lowercase English letters.</li>
</ul>

struct TrieNode {
    bool isEnd;
    int count = 0;
    vector<TrieNode*> child;

    TrieNode() {
        isEnd = false;
        count = 0;
        child.resize(26, NULL);
    }
};

class Solution {
public:
    void addString(TrieNode *root, string s) {
        TrieNode *curr = root;

        for (auto c: s) {
            int ind = c - 'a';
            if (curr->child[ind] == NULL) {
                curr->child[ind] = new TrieNode();
            }

            curr = curr->child[ind];            
        }

        curr->isEnd = true;
        curr->count++;
    }

    bool searchString(TrieNode *root, string s) {
        TrieNode *curr = root;
        int n = s.size();
        
        for (int i = 0; i < n; i++) {            
            int ind = s[i] - 'a';                                    
            curr = curr->child[ind];        

            if (curr->count < 1) return false;
        }        

        return true;
    }

    string longestWord(vector<string>& words) {
        int n = words.size();

        TrieNode *root = new TrieNode();

        for (int i = 0; i < n; i++) {
            addString(root, words[i]);
        }

        set<string> st;

        for (int i = 0; i < n; i++) {
            bool flag = searchString(root, words[i]);
            if (flag) {
                st.insert(words[i]);
            }
        }

        string ans = "";
        int mx = 0;

        for (auto s: st) {
            if (s.size() > mx) {
                mx = s.size(); 
                ans = s;
            }
        }

        return ans;
    }
};
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