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Word Search Problem

Certification: Advanced Level Accuracy: 0% Submissions: 0 Points: 15

Write a C# program to solve the Word Search problem. Given an m x n grid of characters board and a string word, return true if word exists in the grid. The word can be constructed from letters of sequentially adjacent cells, where adjacent cells are horizontally or vertically neighboring. The same letter cell may not be used more than once.

Example 1
    
  
  • Input: board = [["A","B","C","E"],["S","F","C","S"],["A","D","E","E"]], word = "ABCCED"
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  • Output: true
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  • Explanation: 
    
      
      
    • The word "ABCCED" can be found by starting at the top-left A and following these paths:
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    • A → B → C → C → E → D
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Example 2
    
  
  • Input: board = [["A","B","C","E"],["S","F","C","S"],["A","D","E","E"]], word = "SEE"
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  • Output: true
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  • Explanation: 
    
      
      
    • The word "SEE" can be found by starting at the middle S and following this path:
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    • S → E → E
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Constraints
    
  
  • m == board.length
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  • n = board[i].length
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  • 1 <= m, n <= 6
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  • 1 <= word.length <= 15
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  • board and word consists of only lowercase and uppercase English letters
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  • Time Complexity: O(m * n * 4^L) where L is the length of word
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  • Space Complexity: O(L) for the recursion stack
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AlgorithmsBacktracking IBM
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Hint
Solution

Solution Hints

    
  
  • Use depth-first search (DFS) with backtracking
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  • Start the search from every cell in the grid
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  • Mark visited cells to avoid using the same cell multiple times
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  • Explore in all four directions (up, down, left, right) for each cell
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  • Backtrack by unmarking cells when a path doesn't lead to a solution
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Steps to solve by this approach:

 Step 1: Iterate through each cell in the grid as a potential starting point.
 Step 2: For each cell that matches the first character of the word, start a DFS search.
 Step 3: In the DFS function, check if we've found the complete word (base case for success).
 Step 4: Check boundary conditions and whether the current cell matches the expected character.
 Step 5: Mark the current cell as visited to avoid using it again in the same path.
 Step 6: Recursively explore all four adjacent cells (up, down, left, right) to continue the search.
 Step 7: Backtrack by restoring the cell's original value after exploration.

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