some of the early Ch2 exercises from think complexity; now here: github.com/yosemitebandit/think-complexity

graph.go

package graph

type Vertex struct {
	Label string
}

type Edge struct {
	Start Vertex
	End   Vertex
}

type Graph struct {
	vertices    []Vertex
	edges       []Edge
	connections map[Vertex]Vertex
}

func (g *Graph) Add_vertex(v Vertex) {
	g.vertices = append(g.vertices, v)
}

// Connect two vertices.
// Init the connections map if it is empty.
func (g *Graph) connect(v1, v2 Vertex) {
	if g.connections == nil {
		g.connections = make(map[Vertex]Vertex)
	}
	g.connections[v1] = v2
	g.connections[v2] = v1
}

func (g *Graph) Add_edge(e Edge) {
	g.connect(e.Start, e.End)
	g.edges = append(g.edges, e)
}

graph_test.go

package graph

import "testing"

func TestAddVertex(t *testing.T) {
	v1 := Vertex{"v1"}
	g := new(Graph)
	g.Add_vertex(v1)
	if g.vertices[0] != v1 {
		t.Error("expected v1, got ", g.vertices[0])
	}
}

func TestConnect(t *testing.T) {
	v1 := Vertex{"v1"}
	v2 := Vertex{"v2"}
	v3 := Vertex{"v3"}
	v4 := Vertex{"v4"}
	g := new(Graph)
	g.connect(v1, v2)
	g.connect(v3, v4)
	if g.connections[v1] != v2 {
		t.Error("v1 -/-> v2")
	}
	if g.connections[v2] != v1 {
		t.Error("v2 -/-> v1")
	}
	if g.connections[v3] != v4 {
		t.Error("v3 -/-> v4")
	}
	if g.connections[v4] != v3 {
		t.Error("v4 -/-> v3")
	}
}

func TestAddEdge(t *testing.T) {
	v1 := Vertex{"v1"}
	v2 := Vertex{"v2"}
	e1 := Edge{v1, v2}
	g := new(Graph)
	g.Add_edge(e1)
	if g.edges[0] != e1 {
		t.Error("expected e1, got ", g.edges[0])
	}
	if g.connections[v1] != v2 {
		t.Error("v1 -/-> v2")
	}
	if g.connections[v2] != v1 {
		t.Error("v2 -/-> v1")
	}
}

main.go

package main

import (
	"fmt"

	"github.com/yosemitebandit/thinkcomplexity/ch2/graph"
)

func main() {
	v1, v2, v3, v4, v5 := graph.Vertex{"v1"}, graph.Vertex{"v2"}, graph.Vertex{"v3"}, graph.Vertex{"v4"}, graph.Vertex{"v5"}
	e1, e2 := graph.Edge{v1, v2}, graph.Edge{v3, v4}

	g := new(graph.Graph)

	for _, v := range []graph.Vertex{v1, v2, v3, v4, v5} {
		g.Add_vertex(v)
	}
	for _, e := range []graph.Edge{e1, e2} {
		g.Add_edge(e)
	}

	fmt.Println(g)
}