Merge 9adac51 into c969b2c

README.md

@@ -462,4 +462,5 @@ problems from
 * [Day 463](https://github.com/vaskoz/dailycodingproblem-go/issues/937)
 * [Day 464](https://github.com/vaskoz/dailycodingproblem-go/issues/935)
 * [Day 465](https://github.com/vaskoz/dailycodingproblem-go/issues/933)
+* [Day 473](https://github.com/vaskoz/dailycodingproblem-go/issues/939)
 

day473/problem.go

@@ -0,0 +1,23 @@
+package day473
+
+// AdjacencyMatrix is a directed graph adjacency matrix.
+type AdjacencyMatrix map[rune]map[rune]struct{}
+
+// ReverseDirectedGraph reverses all the edges in a given
+// directed graph.
+// Runs in O(N) time and produces a new graph using O(N) space.
+func ReverseDirectedGraph(g AdjacencyMatrix) AdjacencyMatrix {
+	reversed := make(AdjacencyMatrix, len(g))
+
+	for a := range g {
+		for b := range g[a] {
+			if _, found := reversed[b]; !found {
+				reversed[b] = make(map[rune]struct{})
+			}
+
+			reversed[b][a] = struct{}{}
+		}
+	}
+
+	return reversed
+}

day473/problem_test.go

@@ -0,0 +1,48 @@
+package day473
+
+import (
+	"reflect"
+	"testing"
+)
+
+// nolint
+var testcases = []struct {
+	g, reversed AdjacencyMatrix
+}{
+	{
+		AdjacencyMatrix{
+			'A': {
+				'B': struct{}{},
+			},
+			'B': {
+				'C': struct{}{},
+			},
+		},
+		AdjacencyMatrix{
+			'C': {
+				'B': struct{}{},
+			},
+			'B': {
+				'A': struct{}{},
+			},
+		},
+	},
+}
+
+func TestReverseDirectedGraph(t *testing.T) {
+	t.Parallel()
+
+	for _, tc := range testcases {
+		if reversed := ReverseDirectedGraph(tc.g); !reflect.DeepEqual(reversed, tc.reversed) {
+			t.Errorf("Expected %v, got %v", tc.reversed, reversed)
+		}
+	}
+}
+
+func BenchmarkReverseDirectedGraph(b *testing.B) {
+	for i := 0; i < b.N; i++ {
+		for _, tc := range testcases {
+			ReverseDirectedGraph(tc.g)
+		}
+	}
+}