Day427

README.md

@@ -422,4 +422,5 @@ problems from
 * [Day 423](https://github.com/vaskoz/dailycodingproblem-go/issues/854)
 * [Day 424](https://github.com/vaskoz/dailycodingproblem-go/issues/856)
 * [Day 425](https://github.com/vaskoz/dailycodingproblem-go/issues/858)
+* [Day 427](https://github.com/vaskoz/dailycodingproblem-go/issues/861)
 

day427/problem.go

@@ -0,0 +1,90 @@
+package day427
+
+import (
+	"errors"
+)
+
+// Elevation is a map of locations to their elevations.
+type Elevation map[int]int
+
+// PathDistance represents the distance for a particular path.
+type PathDistance map[int]map[int]int
+
+// MaxInt is the largest int.
+const MaxInt = int(^uint(0) >> 1)
+
+var errNotPossible = errors.New("no path possible")
+
+// ErrNotPossible is the error returned if a path doesn't exist.
+func ErrNotPossible() error {
+	return errNotPossible
+}
+
+// ShortestRunnerPath with the condition that the route goes entirely
+// uphill at first, and then entirely downhill.
+// Always starts at location 0 and end at location 0.
+func ShortestRunnerPath(elevations Elevation, paths PathDistance) (int, error) {
+	min := MaxInt
+	startElev := elevations[0]
+
+	for next, distance := range paths[0] {
+		nextElev := elevations[next]
+		if nextElev > startElev {
+			dist, err := shortestRunnerPath(elevations, paths, map[int]struct{}{}, true, next)
+			if err == nil && dist+distance < min {
+				min = dist + distance
+			}
+		}
+	}
+
+	if min == MaxInt {
+		return 0, ErrNotPossible()
+	}
+
+	return min, nil
+}
+
+func shortestRunnerPath(
+	elevations Elevation,
+	paths PathDistance,
+	visited map[int]struct{},
+	up bool,
+	n int) (int, error) {
+	if n == 0 {
+		return 0, nil
+	}
+
+	min := MaxInt
+	currentElevation := elevations[n]
+
+	for next, distance := range paths[n] {
+		if _, visit := visited[next]; !visit {
+			nextElevation := elevations[next]
+			if up && nextElevation > currentElevation {
+				visited[next] = struct{}{}
+				dist, err := shortestRunnerPath(elevations, paths, visited, true, next)
+				totalDist := dist + distance
+
+				if err == nil && totalDist < min {
+					min = totalDist
+				}
+
+				delete(visited, next)
+			} else if nextElevation < currentElevation {
+				visited[next] = struct{}{}
+				dist, err := shortestRunnerPath(elevations, paths, visited, false, next)
+				totalDist := dist + distance
+				if err == nil && totalDist < min {
+					min = totalDist
+				}
+				delete(visited, next)
+			}
+		}
+	}
+
+	if min == MaxInt {
+		return 0, ErrNotPossible()
+	}
+
+	return min, nil
+}

day427/problem_test.go

@@ -0,0 +1,145 @@
+package day427
+
+import "testing"
+
+// nolint
+var testcases = []struct {
+	elevations    Elevation
+	paths         PathDistance
+	shortestRoute int
+	err           error
+}{
+	{
+		Elevation{
+			0: 15,
+			1: 10,
+			2: 25,
+		},
+		PathDistance{
+			0: {
+				2: 5,
+			},
+			1: {
+				0: 1,
+			},
+			2: {
+				1: 7,
+			},
+		},
+		0,
+		ErrNotPossible(),
+	},
+	{
+		Elevation{
+			0: 10,
+			1: 25,
+			2: 15,
+		},
+		PathDistance{
+			0: {
+				1: 15,
+				2: 5,
+			},
+			1: {
+				0: 1,
+			},
+			2: {
+				1: 7,
+				0: 30,
+			},
+		},
+		13,
+		nil,
+	},
+	{
+		Elevation{
+			0: 10,
+			1: 5,
+			2: 7,
+		},
+		PathDistance{
+			0: {
+				1: 5,
+				2: 10,
+			},
+			1: {
+				0: 5,
+			},
+			2: {
+				0: 10,
+			},
+		},
+		0,
+		ErrNotPossible(),
+	},
+	{
+		Elevation{
+			0: 10,
+			1: 5,
+			2: 15,
+		},
+		PathDistance{
+			0: {
+				1: 5,
+				2: 10,
+			},
+			1: {
+				0: 5,
+			},
+			2: {
+				0: 10,
+			},
+		},
+		20,
+		nil,
+	},
+	{
+		Elevation{
+			0: 5,
+			1: 25,
+			2: 15,
+			3: 20,
+			4: 10,
+		},
+		PathDistance{
+			0: {
+				1: 10,
+				2: 8,
+				3: 15,
+			},
+			1: {
+				3: 12,
+			},
+			2: {
+				4: 10,
+			},
+			3: {
+				4: 5,
+				0: 17,
+			},
+			4: {
+				0: 10,
+			},
+		},
+		28,
+		nil,
+	},
+}
+
+func TestShortestRunnerPath(t *testing.T) {
+	t.Parallel()
+
+	for _, tc := range testcases {
+		if result, err := ShortestRunnerPath(tc.elevations, tc.paths); result != tc.shortestRoute || err != tc.err {
+			t.Errorf("Expected (%v,%v), got (%v,%v)", tc.shortestRoute, tc.err, result, err)
+		}
+	}
+}
+
+func BenchmarkShortestRunnerPath(b *testing.B) {
+	for i := 0; i < b.N; i++ {
+		for _, tc := range testcases {
+			ShortestRunnerPath(tc.elevations, tc.paths) // nolint
+		}
+	}
+}