Word Search II

Given an m x n board of characters and a list of strings words, return all words on the board.

Each word must 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 in a word.

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Example 1

o a a n
e t a e
i h k r
i f l v

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: "eat" starts at (1,3) going left. "oath" starts at (0,0) going down-right. "pea" and "rain" are not on the board.

Example 2

a b
c d

Input: board = [["a","b"],["c","d"]], words = ["abcb"]
Output: []
Explanation: "abcb" would require reusing the cell at (0,1), which is not allowed.

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Constraints

• m == board.length
• n == board[i].length
• 1 <= m, n <= 12
• board[i][j] is a lowercase English letter.
• 1 <= words.length <= 3 * 10^4
• 1 <= words[i].length <= 10
• words[i] consists of lowercase English letters.
• All the strings in words are unique.