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Trie (Prefix Tree)

Certification: Intermediate Level Accuracy: 0% Submissions: 0 Points: 10

Write a Java program to implement a Trie (Prefix Tree). A trie is a tree-like data structure used to store a dynamic set of strings, where the keys are usually strings. The Trie should support the following operations:

  • `insert(word)`: Inserts a word into the trie.
  • `search(word)`: Returns true if the word is in the trie, false otherwise.
  • `startsWith(prefix)`: Returns true if there is any word in the trie that starts with the given prefix, false otherwise.
Example 1
    
  
  • Input: 
    
      
      
    • ["Trie", "insert", "search", "search", "startsWith", "insert", "search"]
      • 
      
    • [[], ["apple"], ["apple"], ["app"], ["app"], ["app"], ["app"]]
      • 
    
    
  
    • 
  
  • Output: [null, null, true, false, true, null, true]
    • 
  
  • Explanation: 
    
      
      
    • Initialize a new Trie object
      • 
      
    • Insert the word "apple" into the trie
      • 
      
    • Search for "apple" - returns true as it was inserted
      • 
      
    • Search for "app" - returns false as it wasn't inserted
      • 
      
    • Check if any word starts with "app" - returns true as "apple" starts with "app"
      • 
      
    • Insert the word "app" into the trie
      • 
      
    • Search for "app" - returns true as it was inserted
      • 
    
    
  
    •
Example 2
    
  
  • Input: 
    
      
      
    • ["Trie", "insert", "insert", "insert", "startsWith", "search", "search", "startsWith"]
      •  
      
    • [[], ["hello"], ["world"], ["hi"], ["h"], ["hello"], ["hey"], ["world"]]
      • 
    
    
  
    • 
  
  • Output: [null, null, null, null, true, true, false, false]
    • 
  
  • Explanation: 
    
      
      
    • Initialize a new Trie object
      • 
      
    • Insert the word "hello" into the trie
      • 
      
    • Insert the word "world" into the trie
      • 
      
    • Insert the word "hi" into the trie
      • 
      
    • Check if any word starts with "h" - returns true as "hello" and "hi" start with "h"
      • 
      
    • Search for "hello" - returns true as it was inserted
      • 
      
    • Search for "hey" - returns false as it wasn't inserted
      • 
      
    • Check if any word starts with "world" - returns false as no word starts with "world" (although "world" itself exists)
      • 
    
    
  
    •
Constraints
    
  
  • 1 ≤ word.length, prefix.length ≤ 2000
    • 
  
  • word and prefix consist only of lowercase English letters
    • 
  
  • At most 3 * 10^4 calls in total will be made to insert, search, and startsWith
    • 
  
  • You may assume all inputs are valid
    • 
  
  • Each word consists only of lowercase English letters
    • 
  
  • Time Complexity: 
    
      
      
    • insert: O(m), where m is the length of the word
      • 
      
    • search: O(m), where m is the length of the word
      • 
      
    • startsWith: O(m), where m is the length of the prefix
      • 
    
    
  
    • 
  
  • Space Complexity: O(T), where T is the total number of characters in all inserted words
    •
Trie TreeEYApple
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Hint
Solution

Solution Hints

    
  
  • Use a tree-like data structure where each node represents a character
    • 
  
  • Each node should have a boolean flag to mark the end of a word
    • 
  
  • Each node should have children nodes for all possible next characters
    • 
  
  • Use a TrieNode class to represent each node in the trie
    • 
  
  • For insert, navigate or create nodes for each character and mark the last node as end of word
    • 
  
  • For search, navigate through nodes for each character and check if the last node is marked as end of word
    • 
  
  • For startsWith, navigate through nodes for each character but don't need to check if the last node is end of word
    •

Steps to solve by this approach:

 Step 1: Create a TrieNode class with an array of children nodes and a flag to mark end of word

 Step 2: Initialize the Trie with a root node

 Step 3: For insert, traverse the trie and create new nodes for characters that don't exist

 Step 4: Mark the last node as end of word when insert is complete

 Step 5: Create a helper method to find a node for a given prefix

 Step 6: For search, find the node for the word and check if it's marked as end of word

 Step 7: For startsWith, simply find the node for the prefix without checking if it's end of word

Submitted Code :