Word Search
You are given an m × n grid of letters board and a string word. Return true if word can be traced in the grid, and false otherwise.
To trace a word, start at a cell holding its first letter and move one step at a time to a horizontally or vertically adjacent cell (no diagonals) that holds the next letter. A single cell may not be used twice in the same word.
Letters are case-sensitive: "a" does not match "A". You may change board while searching, as long as you return the right answer.
Constraints
1 <= m, n <= 61 <= word.length <= 15boardandwordcontain only English letters.
Examples
Example 1
Input: board = [["S","E","E","D"],["T","A","R","S"],["O","N","E","X"]], word = "STARE" Output: true
S (row 0) → T below it → A to the right → R → E above R. Every step moves to a neighbouring cell.
Example 2
Input: board = [["S","E","E","D"],["T","A","R","S"],["O","N","E","X"]], word = "TONES" Output: false
T → O → N → E works, but no S touches that E, so the word can't be finished.
Example 3
Input: board = [["A","B"],["C","D"]], word = "ABA" Output: false
The board has only one A, and a cell can't be used twice in the same word.
JavaScript you'll use: Graphs and grids in JavaScript Recursion, the call stack and memoization Strings and characters
/**
* @param {string[][]} board
* @param {string} word
* @return {boolean}
*/
function exist(board, word) {
}
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