royling · April 24, 2021 14:51 · Apr 24, 2021 · Apr 24, 2021 · Apr 24, 2021 · Apr 24, 2021
diff --git a/rot13_reader.go b/rot13_reader.go
@@ -0,0 +1,49 @@
+package main
+
+import (
+	"io"
+	"os"
+	"strings"
+)
+
+type rot13Reader struct {
+	r io.Reader
+}
+
+func subst(b byte) byte {
+	var (
+		alpha bool
+		start byte
+	)
+	switch {
+	case b >= 'a' && b <= 'z':
+		alpha = true
+		start = 'a'
+	case b >= 'A' && b <= 'Z':
+		alpha = true
+		start = 'A'
+	}
+	if alpha {
+		return (b+13-start)%26 + start
+	}
+	return b
+}
+
+func (rot13 *rot13Reader) Read(b []byte) (int, error) {
+	n, err := rot13.r.Read(b)
+	if err == io.EOF {
+		return 0, err
+	}
+
+	for i, c := range b {
+		b[i] = subst(c)
+	}
+	return n, nil
+}
+
+func main() {
+	s := strings.NewReader("Lbh penpxrq gur pbqr!")
+	r := rot13Reader{s}
+	io.Copy(os.Stdout, &r)
+  // You cracked the code!
+}
diff --git a/io_reader.go b/io_reader.go
@@ -0,0 +1,15 @@
+package main
+
+import "golang.org/x/tour/reader"
+
+type MyReader struct{}
+
+// TODO: Add a Read([]byte) (int, error) method to MyReader.
+func (r MyReader) Read(b []byte) (int, error) {
+	b[0] = 'A'
+	return 1, nil
+}
+
+func main() {
+	reader.Validate(MyReader{})
+}
diff --git a/fibonacci.go b/fibonacci.go
@@ -0,0 +1,21 @@
+package main
+
+import "fmt"
+
+// fibonacci is a function that returns
+// a function that returns an int.
+func fibonacci() func() int {
+	a, b := 0, 1
+	return func() int {
+		i := a
+		a, b = b, a+b
+		return i
+	}
+}
+
+func main() {
+	f := fibonacci()
+	for i := 0; i < 10; i++ {
+		fmt.Println(f())
+	}
+}
diff --git a/map.go b/map.go
@@ -21,3 +21,25 @@ func WordCount(s string) map[string]int {
 func main() {
 	wc.Test(WordCount)
 }
+
+/*
+var m2 = map[int]string{
+	1: "a",
+	2: "b",
+}
+
+// Pointer as key type
+var m3 = map[*Vertex]string {
+	&Vertex{40.68433, -74.39967,}: "Bell",
+	&Vertex{37.42202, -122.08408,}: "Google",
+	nil: "nil",
+}
+
+// Pointer as value type
+var m4 = map[string]*Vertex {
+	"Bell Labs": &Vertex{40.68433, -74.39967},
+	"Google":    &Vertex{37.42202, -122.08408},
+}
+
+// Cannot omit type name `Vertex` if pointer is used as key/value type!
+*/
diff --git a/map.go b/map.go
@@ -9,9 +9,9 @@ import (
 func WordCount(s string) map[string]int {
 	m := make(map[string]int)
 	for _, w := range strings.Fields(s) {
-		if _, present := m[w]; !present {
-			m[w] = 0
-		}
+		//if _, present := m[w]; !present {
+		//	m[w] = 0
+		//}
 
 		m[w] += 1
 	}

diff --git a/map.go b/map.go
@@ -9,10 +9,10 @@ import (
 func WordCount(s string) map[string]int {
 	m := make(map[string]int)
 	for _, w := range strings.Fields(s) {
-		_, present := m[w]
-		if !present {
+		if _, present := m[w]; !present {
 			m[w] = 0
 		}
+
 		m[w] += 1
 	}
 	return m

diff --git a/map.go b/map.go
@@ -0,0 +1,23 @@
+package main
+
+import (
+	"strings"
+
+	"golang.org/x/tour/wc"
+)
+
+func WordCount(s string) map[string]int {
+	m := make(map[string]int)
+	for _, w := range strings.Fields(s) {
+		_, present := m[w]
+		if !present {
+			m[w] = 0
+		}
+		m[w] += 1
+	}
+	return m
+}
+
+func main() {
+	wc.Test(WordCount)
+}
diff --git a/gotour_slice.go → slice.go b/gotour_slice.go → slice.go
diff --git a/gotour_slice.go b/gotour_slice.go
@@ -0,0 +1,31 @@
+package main
+
+import "golang.org/x/tour/pic"
+
+type Selector func(int, int) int
+
+type Renderer func(int, int) [][]uint8
+
+func PicSelector(f Selector) Renderer {
+	return func(dx, dy int) [][]uint8 {
+		var res [][]uint8
+
+		for y := 0; y < dy; y++ {
+			var e []uint8
+			for x := 0; x < dx; x++ {
+				v := uint8(f(x, y))
+				e = append(e, v)
+			}
+			res = append(res, e)
+		}
+
+		return res
+	}
+}
+
+func main() {
+	pic.Show(PicSelector(func(x, y int) int {
+		return (x + y) * (x - y)
+	}))
+
+}