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// @Title: 单词搜索 (Word Search)
// @Author: 15816537946@163.com
// @Date: 2020-12-06 12:49:38
// @Runtime: 4 ms
// @Memory: 3.2 MB
func exist(board [][]byte, word string) bool {
	if word == "" {
		return false
	}
	m := len(board)
	if m == 0 {
		return false
	}
	n := len(board[0])
	if n == 0 {
		return false
	}
	var bfs func(int, int, int) bool
	bfs = func(r, c, index int) bool {
		if index == len(word) {
			return true
		}
		if r < 0 || r >= m || c < 0 || c >= n || word[index] != board[r][c] {
			return false
		}

		temp := board[r][c]
		board[r][c] = 0
		if bfs(r+1, c, index+1) || bfs(r, c+1, index+1) || bfs(r-1, c, index+1) || bfs(r, c-1, index+1) {
			return true
		}
		board[r][c] = temp

		return false
	}

	for i := range board {
		for j := range board[0] {
			if bfs(i, j, 0) {
				return true
			}
		}
	}
	return false
}