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Word Search II using Trie

Certification: Advanced Level Accuracy: 100% Submissions: 1 Points: 15

Write a Java program to find all words in a given board of characters. The words can be constructed from letters of adjacent cells (horizontally, vertically, or diagonally), and each letter cell can only be used once in a word. You are given a 2D board of characters and a list of words to find.

Example 1
    
  
  • Input: 
board = [

     ['o','a','a','n'],

     ['e','t','a','e'],

     ['i','h','k','r'],

     ['i','f','l','v']
]

  • words = ["oath","pea","eat","rain"]
    • 
  
  • Output: ["eat","oath"]
    • 
  
  • Explanation: For "oath", we can find it by starting at board[0][0] ('o') and moving to adjacent cells: 'a' at [0][1], 't' at [1][1], and 'h' at [2][1]. For "eat", we can find a path through adjacent cells.
    •
Example 2
    
  
  • Input: 
board = [

     ['a','b'],

     ['c','d']
]

    words = ["abcd","abad","acbd","abdc"]
    • 
  
  • Output: ["abcd"]
    • 
  
  • Explanation: We can find "abcd" by starting at board[0][0] ('a'), then 'b' at [0][1], then 'c' at [1][0], and finally 'd' at [1][1].
    •
Constraints
    
  
  • 1 <= board.length, board[i].length <= 12
    • 
  
  • board[i][j] is a lowercase English letter
    • 
  
  • 1 <= words.length <= 3 * 10^4
    • 
  
  • 1 <= words[i].length <= 10
    • 
  
  • All words in the input list are unique
    • 
  
  • Time Complexity: O(M * N * 4^L), where M and N are the dimensions of the board and L is the maximum length of a word
    • 
  
  • Space Complexity: O(K), where K is the total number of characters in all words
    •
Trie TreeMicrosoftWalmart
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Hint
Solution

Solution Hints

    
  
  • Build a Trie data structure from the list of words to search for
    • 
  
  • Use a depth-first search (DFS) starting from each cell in the board
    • 
  
  • During DFS, match characters on the board with nodes in the Trie
    • 
  
  • Use a visited matrix to avoid reusing the same cell for a single word
    • 
  
  • When a complete word is found, add it to the result set
    • 
  
  • Use a set to avoid adding duplicate words to the result
    • 
  
  • Optimize by pruning the Trie as words are found
    •

Steps to solve by this approach:

 Step 1: Create a Trie data structure to store all the words that we need to search for.

 Step 2: Create a TrieNode class with an array of 26 children (representing the lowercase English alphabet) and a string field to store the complete word.

 Step 3: Build the Trie by inserting all words from the input array.

 Step 4: For each cell in the board, start a depth-first search to find words from the Trie.

 Step 5: During DFS, mark cells as visited to avoid reusing them in the same word search.

 Step 6: When a complete word is found in the Trie, add it to the result list and set its reference to null in the Trie to avoid duplicates.

 Step 7: Restore the board state after exploring each path to ensure other searches can use those cells.

Submitted Code :