package q79

func search(board [][]byte, word string, prefixLen, row, col int) bool {
	if row < 0 || col < 0 || row >= len(board) || col >= len(board[0]) {
		return false
	}
	if word[prefixLen] != board[row][col] {
		return false
	}
	if prefixLen+1 == len(word) {
		return true
	}

	c := board[row][col]
	board[row][col] = '#'
	yes := false ||
		search(board, word, prefixLen+1, row, col+1) ||
		search(board, word, prefixLen+1, row, col-1) ||
		search(board, word, prefixLen+1, row+1, col) ||
		search(board, word, prefixLen+1, row-1, col)

	board[row][col] = c
	return yes
}

func exist(board [][]byte, word string) bool {
	w, h := len(board[0]), len(board)
	if len(word) > w*h {
		return false
	}
	charFreq := make([]int, 26*2)
	idx := func(b byte) byte {
		if b >= 'a' {
			return b - 'a' + 26
		}
		return b - 'A'
	}
	for row := range board {
		for col := range board[0] {
			charFreq[idx(board[row][col])]++
		}
	}
	for i := range len(word) {
		ii := idx(word[i])
		charFreq[ii]--
		if charFreq[ii] < 0 {
			return false
		}
	}

	for row := range board {
		for col := range board[0] {
			if search(board, word, 0, row, col) {
				return true
			}
		}
	}
	return false
}

var _ = exist