Word Search II

Write a C program to find all words from a given dictionary that can be formed by sequentially adjacent letters on a 2D board. Letters can be used more than once, but each cell in a single word search cannot be used more than once. Use Trie data structure for efficient word searching.

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: 
Build a Trie from the dictionary words. 
For each cell in the board, start DFS to find words. 
"eat" can be found starting from board[1][1] → board[1][2] → board[0][2]. 
"oath" can be found starting from board[0][0] → board[0][1] → board[1][1] → board[1][0].
    

Example 2

      
Input: board = [["a","b"],["c","d"]], words = ["abcb"]
      
Output: []
      
Explanation: 
Build a Trie from the dictionary word "abcb". 
Search for "abcb" on the board using DFS. 
No valid path exists to form "abcb" without reusing cells. 
Therefore, return empty result.
    

Constraints

      
m == board.length, n == board[i].length
      
1 ≤ m, n ≤ 12
      
1 ≤ words.length ≤ 3 * 10^4
      
1 ≤ words[i].length ≤ 10
      
Time Complexity: O(M*N*4^L) where L is maximum word length
      
Space Complexity: O(ALPHABET_SIZE * N * L) for Trie