add new solutions

solutions/9/q909/solution.go

@@ -0,0 +1,50 @@
+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