Day229

README.md

@@ -239,6 +239,7 @@ problems from
 * [Day 226](https://github.com/vaskoz/dailycodingproblem-go/issues/467)
 * [Day 227](https://github.com/vaskoz/dailycodingproblem-go/issues/469)
 * [Day 228](https://github.com/vaskoz/dailycodingproblem-go/issues/470)
+* [Day 229](https://github.com/vaskoz/dailycodingproblem-go/issues/472)
 * [Day 230](https://github.com/vaskoz/dailycodingproblem-go/issues/473)
 * [Day 231](https://github.com/vaskoz/dailycodingproblem-go/issues/475)
 * [Day 232](https://github.com/vaskoz/dailycodingproblem-go/issues/477)

day229/problem.go

@@ -0,0 +1,42 @@
+package day229
+
+// Jump represents the movement that happens either up or down.
+// Ladders give you a boost up, while a Snake lowers your position.
+type Jump struct {
+	From, To int
+}
+
+// SnakesAndLaddersFewestTurns by playing all games.
+func SnakesAndLaddersFewestTurns(ladders, snakes []Jump, maxDepth int) int {
+	jumps := make(map[int]int, len(ladders)+len(snakes))
+	for _, j := range ladders {
+		jumps[j.From] = j.To
+	}
+	for _, j := range snakes {
+		jumps[j.From] = j.To
+	}
+	return snakesAndLaddersFewestTurns(jumps, 0, 0, int(^uint(0)>>1), maxDepth)
+}
+
+func snakesAndLaddersFewestTurns(jumps map[int]int, pos, depth, bestSoFar, maxDepth int) int {
+	if pos == 100 {
+		return depth
+	} else if depth > maxDepth || depth > bestSoFar {
+		return bestSoFar
+	}
+	for roll := 6; roll >= 0; roll-- {
+		next := pos + roll
+		if jumpPos, found := jumps[next]; found && jumpPos < pos { // avoid all snakes
+			continue
+		} else if found && jumpPos > pos {
+			next = jumpPos
+		}
+		if next > 100 {
+			break
+		}
+		if turns := snakesAndLaddersFewestTurns(jumps, next, depth+1, bestSoFar, maxDepth); turns < bestSoFar {
+			bestSoFar = turns
+		}
+	}
+	return bestSoFar
+}

day229/problem_test.go

@@ -0,0 +1,15 @@
+package day229
+
+import "testing"
+
+func TestSnakesAndLaddersFewestTurns(t *testing.T) {
+	t.Parallel()
+	fewestTurns := SnakesAndLaddersFewestTurns(
+		[]Jump{{1, 38}, {4, 14}, {9, 31}, {21, 42}, {28, 84}, {36, 44}, {51, 67}, {71, 91}, {80, 100}},
+		[]Jump{{16, 6}, {48, 26}, {49, 11}, {56, 53}, {62, 19}, {64, 60}, {87, 24}, {93, 73}, {95, 75}, {98, 78}},
+		6,
+	)
+	if fewestTurns != 7 {
+		t.Errorf("on the original game board best is 7, got %v", fewestTurns)
+	}
+}