#261 Search for Word

Given a 2D board of characters and a word, determine if the word exists in the board.

Rules for word existence:

• Word can be constructed from letters of adjacent cells
• Adjacent means horizontally or vertically neighboring
• Same cell cannot be used more than once
• Board contains only English letters (case-sensitive)

Constraints:

• 1 ≤ board dimensions ≤ 5
• 1 ≤ word.length ≤ 10
• Board and word contain only English letters

Examples:

// Example 1:

const board1 = [
  ["A","B","C","D"],
  ["S","A","A","T"],
  ["A","C","A","E"]
];
console.log(exist(board1, "CAT"));
// Output: true

// Explanation: Can form "CAT" using adjacent cells


// Example 2:

const board2 = [
  ["A","B","C","D"],
  ["S","A","A","T"],
  ["A","C","A","E"]
];
console.log(exist(board2, "BAT"));
// Output: false

// Explanation: Cannot form "BAT" using adjacent cells