## Algorithm

Problem Name: 720. Longest Word in Dictionary

Given an array of strings `words` representing an English Dictionary, return 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.

Note that the word should be built from left to right with each additional character being added to the end of a previous word.

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".
```

Constraints:

• `1 <= words.length <= 1000`
• `1 <= words[i].length <= 30`
• `words[i]` consists of lowercase English letters.

## Code Examples

### #1 Code Example with C++ Programming

```Code - C++ Programming```

``````
class Solution {
public:
string longestWord(vector& words) {
string res = "";
unordered_map>m;
for(auto s: words) m[s.size()].insert(s);
for(auto s: words){
int i = 1;
while(i < s.size() && m[i].count(s.substr(0, i))) i++;
if(i == s.size() && s.size() >= res.size()) res = s.size() > res.size() ? s : min(s, res);
}
return res;
}
};
``````
Copy The Code &

Input

cmd
words = ["w","wo","wor","worl","world"]

Output

cmd
"world"

### #2 Code Example with Javascript Programming

```Code - Javascript Programming```

``````
const longestWord = function(words) {
if(words == null || words.length === 0) return ''
words.sort()
const s = new Set()
let res = ''
for(let i = 0, len = words.length; i < len; i++) {
const w = words[i]
if(w.length === 1 || s.has(w.slice(0, w.length - 1))) {
res = w.length > res.length ? w : res
}
}
return res
};
``````
Copy The Code &

Input

cmd
words = ["w","wo","wor","worl","world"]

Output

cmd
"world"

### #3 Code Example with Python Programming

```Code - Python Programming```

``````
class Solution:
def longestWord(self, words):
"""
:type words: List[str]
:rtype: str
"""
for w in sorted(words, key = lambda x: (-len(x), x)):
if all([True if w[:i] in set(words) - {w} else False for i in range(1, len(w))]): return w
return ""
``````
Copy The Code &

Input

cmd
words = ["a","banana","app","appl","ap","apply","apple"]

Output

cmd
"apple"

### #4 Code Example with C# Programming

```Code - C# Programming```

``````
using System.Collections.Generic;

namespace LeetCode
{
public class _0720_LongestWordInDictionary
{
public string LongestWord(string[] words)
{
var root = new Trie() { Finished = true };
foreach (var word in words)
{
var current = root;
foreach (var ch in word)
{
if (current.Children[ch - 'a'] == null)
current.Children[ch - 'a'] = new Trie();

current = current.Children[ch - 'a'];
}

current.Finished = true;
current.Word = word;
}

var result = string.Empty;
var stack = new Stack();
stack.Push(root);
while (stack.Count > 0)
{
var node = stack.Pop();
if (node.Finished)
{
if (node.Word.Length >= result.Length)
result = node.Word;
for (int i = 0; i < 26; i++)
{
if (node.Children[i] != null)
stack.Push(node.Children[i]);
}
}
}

return result;
}

public class Trie
{
public Trie[] Children = new Trie;
public bool Finished = false;
public string Word = string.Empty;
}
}
}
``````
Copy The Code &

Input

cmd
words = ["a","banana","app","appl","ap","apply","apple"]

Output

cmd
"apple"