From a5831193a8316d077cf9d187f7d18a8fd8442688 Mon Sep 17 00:00:00 2001
From: Ryan Cavicchioni <ryan@cavi.cc>
Date: Sun, 16 Feb 2020 14:49:53 -0600
Subject: [PATCH] last exercises

---
 exercise-equivalent-binary-trees.go |  55 +++++++++++++++
 exercise-web-crawler.go             | 106 ++++++++++++++++++++++++++++
 mutex-counter.go                    |  39 ++++++++++
 3 files changed, 200 insertions(+)
 create mode 100644 exercise-equivalent-binary-trees.go
 create mode 100644 exercise-web-crawler.go
 create mode 100644 mutex-counter.go

diff --git a/exercise-equivalent-binary-trees.go b/exercise-equivalent-binary-trees.go
new file mode 100644
index 0000000..02a991b
--- /dev/null
+++ b/exercise-equivalent-binary-trees.go
@@ -0,0 +1,55 @@
+package main
+
+import "golang.org/x/tour/tree"
+
+import (
+    "fmt"
+    "sort"
+)
+
+// Walk walks the tree t sending all values
+// from the tree to the channel ch.
+func Walk(t *tree.Tree, ch chan int) {
+    if t.Value > 0 {
+        ch <- t.Value
+    }
+    if t.Left != nil {
+        go Walk(t.Left, ch)
+    }
+    if t.Right != nil {
+        go Walk(t.Right, ch)
+    }
+}
+
+// Same determines whether the trees
+// t1 and t2 contain the same values.
+func Same(t1, t2 *tree.Tree) bool {
+    s1 := make([]int, 10)
+    s2 := make([]int, 10)
+    ch1 := make(chan int)
+    ch2 := make(chan int)
+    go Walk(t1, ch1)
+    go Walk(t2, ch2)
+    for i := 0; i < 10; i++ {
+        s1 = append(s1, <- ch1)
+        s2 = append(s2, <- ch2)
+    }
+    sort.Ints(s1)
+    sort.Ints(s2)
+    for i, _ := range s1 {
+        if s1[i] != s2[i] {
+            return false
+        }
+    }
+    return true
+}
+
+func main() {
+    ch := make(chan int)
+    go Walk(tree.New(1), ch)
+    for i := 0; i < 10; i++ {
+        fmt.Println(<- ch)
+    }
+    fmt.Println(Same(tree.New(1), tree.New(1)))
+    fmt.Println(Same(tree.New(1), tree.New(2)))
+}
diff --git a/exercise-web-crawler.go b/exercise-web-crawler.go
new file mode 100644
index 0000000..74e390f
--- /dev/null
+++ b/exercise-web-crawler.go
@@ -0,0 +1,106 @@
+package main
+
+import (
+    "fmt"
+    "sync"
+)
+
+type SafeCounter struct {
+    v map[string]int
+    mux  sync.Mutex
+}
+
+func (c *SafeCounter) Inc(key string) {
+    c.mux.Lock()
+    defer c.mux.Unlock()
+    c.v[key]++
+}
+
+func (c *SafeCounter) Value(key string) int {
+    c.mux.Lock()
+    defer c.mux.Unlock()
+    return c.v[key]
+}
+
+type Fetcher interface {
+    // Fetch returns the body of URL and
+    // a slice of URLs found on that page.
+    Fetch(url string) (body string, urls []string, err error)
+}
+
+// Crawl uses fetcher to recursively crawl
+// pages starting with url, to maximum of depth.
+func Crawl(url string, depth int, fetcher Fetcher, c SafeCounter) {
+    // TODO: Fetch URLs in parallel.
+    // TODO: Don't fetch the same URL twice.
+    // This implementation doesn't do either.
+    if depth <= 0 {
+        return
+    }
+    if c.Value(url) > 0 {
+        return
+    }
+    body, urls, err := fetcher.Fetch(url)
+    if err != nil {
+        fmt.Println(err)
+        return
+    }
+    fmt.Printf("found: %s %q\n", url, body)
+    for _, u := range urls {
+        go Crawl(u, depth-1, fetcher, c)
+    }
+}
+
+func main() {
+    c := SafeCounter{v: make(map[string]int)}
+    Crawl("https://www.golang.com/", 4, fetcher, c)
+}
+
+type fakeFetcher map[string]*fakeResult
+
+// fakeFetcher is Fetcher that returns canned results.
+type fakeResult struct {
+    body string
+    urls []string
+}
+
+func (f fakeFetcher) Fetch(url string) (string, []string, error) {
+    if res, ok := f[url]; ok {
+        return res.body, res.urls, nil
+    }
+    return "", nil, fmt.Errorf("not found: %s", url)
+}
+
+// fetcher is a populated fakeFetcher.
+var fetcher = fakeFetcher{
+	"https://golang.org/": &fakeResult{
+		"The Go Programming Language",
+		[]string{
+			"https://golang.org/pkg/",
+			"https://golang.org/cmd/",
+		},
+	},
+	"https://golang.org/pkg/": &fakeResult{
+		"Packages",
+		[]string{
+			"https://golang.org/",
+			"https://golang.org/cmd/",
+			"https://golang.org/pkg/fmt/",
+			"https://golang.org/pkg/os/",
+		},
+	},
+	"https://golang.org/pkg/fmt/": &fakeResult{
+		"Package fmt",
+		[]string{
+			"https://golang.org/",
+			"https://golang.org/pkg/",
+		},
+	},
+	"https://golang.org/pkg/os/": &fakeResult{
+		"Package os",
+		[]string{
+			"https://golang.org/",
+			"https://golang.org/pkg/",
+		},
+	},
+}
diff --git a/mutex-counter.go b/mutex-counter.go
new file mode 100644
index 0000000..1f7aec9
--- /dev/null
+++ b/mutex-counter.go
@@ -0,0 +1,39 @@
+package main
+
+import (
+    "fmt"
+    "sync"
+    "time"
+)
+
+// SafeCounter is safe to use concurrently
+type SafeCounter struct {
+    v   map[string]int
+    mux sync.Mutex
+}
+
+// Inc increments the coutner for the given key
+func (c *SafeCounter) Inc(key string) {
+    c.mux.Lock()
+    // Lock so only one goroutine at a time can access the map c.v
+    c.v[key]++
+    c.mux.Unlock()
+}
+
+// Value returns the current value of the counter for the given key
+func (c *SafeCounter) Value(key string) int {
+    c.mux.Lock()
+    // Lock so only one goroutine at a time can access the map c.v
+    defer c.mux.Unlock()
+    return c.v[key]
+}
+
+func main() {
+    c := SafeCounter{v: make(map[string]int)}
+    for i := 0; i < 1000; i++ {
+        go c.Inc("somekey")
+    }
+
+    time.Sleep(time.Second)
+    fmt.Println(c.Value("somekey"))
+}