package q909

func coord(n, num int) (x, y int) {
	num -= 1
	row := num / n
	y = n - row - 1
	x = num % n
	if row%2 == 1 {
		x = n - 1 - x
	}
	return
}

func snakesAndLadders(board [][]int) int {
	n, sqN := len(board), len(board)*len(board)
	leastRolls := make([]int, sqN)
	if len(leastRolls) == 1 {
		return 0
	}

	queue := make([]int, 0, sqN)
	queue = append(queue, 1)
	for ; len(queue) > 0; queue = queue[1:] {
		cur := queue[0]
		for dist := 1; dist <= 6 && cur+dist <= sqN; dist++ {
			next := cur + dist
			x, y := coord(n, next)
			if board[y][x] != -1 {
				next = board[y][x]
			}
			rolls := leastRolls[cur-1] + 1

			if (next > 1 && leastRolls[next-1] == 0) || rolls < leastRolls[next-1] {
				leastRolls[next-1] = rolls
				if next == sqN {
					return rolls
				}
				queue = append(queue, next)
			}
		}
	}

	l := leastRolls[sqN-1]
	if l == 0 {
		return -1
	}
	return 0
}

var _ = snakesAndLadders