720. Longest Word in Dictionary

Problem Link

Description

---

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.

Solution

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Python3

class TrieNode:
    def __init__(self):
        self.mp = [None] * 26
        self.end = False
 
class Trie:
 
    def __init__(self):
        """
        Initialize your data structure here.
        """
        self.root = TrieNode()
        self.ans = collections.defaultdict(int)
 
 
    def insert(self, word: str):
        """
        Inserts a word into the trie.
        """
        curr = self.root
        n = len(word)
        for i in range(n):
            index = ord(word[i]) - ord('a')
            if not curr.mp[index]:
                curr.mp[index] = TrieNode()
 
            curr = curr.mp[index]
 
        curr.end = True
        
    def search(self):
        self.searchR(self.root)
 
    def searchR(self, node, word = "", level = 0):
        """
        Returns if the word is in the trie.
        """
        
        if node.end and not self.ans[level]:
            self.ans[level] = word
        
        if self.isLastNode(node): return
        
        for i in range(26):
            if node.mp[i] and node.mp[i].end: 
                word += chr(97+i)
                self.searchR(node.mp[i], word, level + 1)
                word = word[:-1]
    
    def isLastNode(self, node):
        for i in range(26):
            if node.mp[i]: return False
        
        return True
        
 
 
class Solution:
    def longestWord(self, words: List[str]) -> str:
        trie = Trie()
        
        for w in words:
            trie.insert(w)
        
        trie.search()
        res = trie.ans
        
        return res[max(res)]