From 103d89b8bcf3b49cab829c7bee8b9691ed7f8cca Mon Sep 17 00:00:00 2001
From: Jamal Carvalho <jamal@golang.org>
Date: Wed, 27 Oct 2021 18:56:01 +0000
Subject: [PATCH] go.dev: fix go playground on homepage

Copied the playground example files to the go.dev content
directory to fix the homepage playground. This works locally
because requests to /doc are passed to the golang.org content
directory but breaks on app engine when requests go to go.dev/doc.

Change-Id: I858b7fca905bbacd0acbf8ea33d1a5188fbd3773
Reviewed-on: https://go-review.googlesource.com/c/website/+/359214
Trust: Jamal Carvalho <jamal@golang.org>
Run-TryBot: Jamal Carvalho <jamal@golang.org>
Reviewed-by: Julie Qiu <julie@golang.org>
Reviewed-by: Dmitri Shuralyov <dmitshur@golang.org>
TryBot-Result: Go Bot <gobot@golang.org>
Website-Publish: DO NOT USE <dmitshur@google.com>
---
 go.dev/_content/doc/play/fib.go       |  19 +++++
 go.dev/_content/doc/play/hello.go     |   9 ++
 go.dev/_content/doc/play/life.go      | 113 +++++++++++++++++++++++++
 go.dev/_content/doc/play/peano.go     |  88 +++++++++++++++++++
 go.dev/_content/doc/play/pi.go        |  34 ++++++++
 go.dev/_content/doc/play/sieve.go     |  36 ++++++++
 go.dev/_content/doc/play/solitaire.go | 117 ++++++++++++++++++++++++++
 go.dev/_content/doc/play/tree.go      | 100 ++++++++++++++++++++++
 8 files changed, 516 insertions(+)
 create mode 100644 go.dev/_content/doc/play/fib.go
 create mode 100644 go.dev/_content/doc/play/hello.go
 create mode 100644 go.dev/_content/doc/play/life.go
 create mode 100644 go.dev/_content/doc/play/peano.go
 create mode 100644 go.dev/_content/doc/play/pi.go
 create mode 100644 go.dev/_content/doc/play/sieve.go
 create mode 100644 go.dev/_content/doc/play/solitaire.go
 create mode 100644 go.dev/_content/doc/play/tree.go

diff --git a/go.dev/_content/doc/play/fib.go b/go.dev/_content/doc/play/fib.go
new file mode 100644
index 00000000..19e47210
--- /dev/null
+++ b/go.dev/_content/doc/play/fib.go
@@ -0,0 +1,19 @@
+package main
+
+import "fmt"
+
+// fib returns a function that returns
+// successive Fibonacci numbers.
+func fib() func() int {
+	a, b := 0, 1
+	return func() int {
+		a, b = b, a+b
+		return a
+	}
+}
+
+func main() {
+	f := fib()
+	// Function calls are evaluated left-to-right.
+	fmt.Println(f(), f(), f(), f(), f())
+}
diff --git a/go.dev/_content/doc/play/hello.go b/go.dev/_content/doc/play/hello.go
new file mode 100644
index 00000000..3badf125
--- /dev/null
+++ b/go.dev/_content/doc/play/hello.go
@@ -0,0 +1,9 @@
+// You can edit this code!
+// Click here and start typing.
+package main
+
+import "fmt"
+
+func main() {
+	fmt.Println("Hello, 世界")
+}
diff --git a/go.dev/_content/doc/play/life.go b/go.dev/_content/doc/play/life.go
new file mode 100644
index 00000000..51afb61f
--- /dev/null
+++ b/go.dev/_content/doc/play/life.go
@@ -0,0 +1,113 @@
+// An implementation of Conway's Game of Life.
+package main
+
+import (
+	"bytes"
+	"fmt"
+	"math/rand"
+	"time"
+)
+
+// Field represents a two-dimensional field of cells.
+type Field struct {
+	s    [][]bool
+	w, h int
+}
+
+// NewField returns an empty field of the specified width and height.
+func NewField(w, h int) *Field {
+	s := make([][]bool, h)
+	for i := range s {
+		s[i] = make([]bool, w)
+	}
+	return &Field{s: s, w: w, h: h}
+}
+
+// Set sets the state of the specified cell to the given value.
+func (f *Field) Set(x, y int, b bool) {
+	f.s[y][x] = b
+}
+
+// Alive reports whether the specified cell is alive.
+// If the x or y coordinates are outside the field boundaries they are wrapped
+// toroidally. For instance, an x value of -1 is treated as width-1.
+func (f *Field) Alive(x, y int) bool {
+	x += f.w
+	x %= f.w
+	y += f.h
+	y %= f.h
+	return f.s[y][x]
+}
+
+// Next returns the state of the specified cell at the next time step.
+func (f *Field) Next(x, y int) bool {
+	// Count the adjacent cells that are alive.
+	alive := 0
+	for i := -1; i <= 1; i++ {
+		for j := -1; j <= 1; j++ {
+			if (j != 0 || i != 0) && f.Alive(x+i, y+j) {
+				alive++
+			}
+		}
+	}
+	// Return next state according to the game rules:
+	//   exactly 3 neighbors: on,
+	//   exactly 2 neighbors: maintain current state,
+	//   otherwise: off.
+	return alive == 3 || alive == 2 && f.Alive(x, y)
+}
+
+// Life stores the state of a round of Conway's Game of Life.
+type Life struct {
+	a, b *Field
+	w, h int
+}
+
+// NewLife returns a new Life game state with a random initial state.
+func NewLife(w, h int) *Life {
+	a := NewField(w, h)
+	for i := 0; i < (w * h / 4); i++ {
+		a.Set(rand.Intn(w), rand.Intn(h), true)
+	}
+	return &Life{
+		a: a, b: NewField(w, h),
+		w: w, h: h,
+	}
+}
+
+// Step advances the game by one instant, recomputing and updating all cells.
+func (l *Life) Step() {
+	// Update the state of the next field (b) from the current field (a).
+	for y := 0; y < l.h; y++ {
+		for x := 0; x < l.w; x++ {
+			l.b.Set(x, y, l.a.Next(x, y))
+		}
+	}
+	// Swap fields a and b.
+	l.a, l.b = l.b, l.a
+}
+
+// String returns the game board as a string.
+func (l *Life) String() string {
+	var buf bytes.Buffer
+	for y := 0; y < l.h; y++ {
+		for x := 0; x < l.w; x++ {
+			b := byte(' ')
+			if l.a.Alive(x, y) {
+				b = '*'
+			}
+			buf.WriteByte(b)
+		}
+		buf.WriteByte('\n')
+	}
+	return buf.String()
+}
+
+func main() {
+	l := NewLife(40, 15)
+	for i := 0; i < 300; i++ {
+		l.Step()
+		fmt.Print("\x0c", l) // Clear screen and print field.
+		time.Sleep(time.Second / 30)
+	}
+}
diff --git a/go.dev/_content/doc/play/peano.go b/go.dev/_content/doc/play/peano.go
new file mode 100644
index 00000000..214fe1b6
--- /dev/null
+++ b/go.dev/_content/doc/play/peano.go
@@ -0,0 +1,88 @@
+// Peano integers are represented by a linked
+// list whose nodes contain no data
+// (the nodes are the data).
+// http://en.wikipedia.org/wiki/Peano_axioms
+
+// This program demonstrates that Go's automatic
+// stack management can handle heavily recursive
+// computations.
+
+package main
+
+import "fmt"
+
+// Number is a pointer to a Number
+type Number *Number
+
+// The arithmetic value of a Number is the
+// count of the nodes comprising the list.
+// (See the count function below.)
+
+// -------------------------------------
+// Peano primitives
+
+func zero() *Number {
+	return nil
+}
+
+func isZero(x *Number) bool {
+	return x == nil
+}
+
+func add1(x *Number) *Number {
+	e := new(Number)
+	*e = x
+	return e
+}
+
+func sub1(x *Number) *Number {
+	return *x
+}
+
+func add(x, y *Number) *Number {
+	if isZero(y) {
+		return x
+	}
+	return add(add1(x), sub1(y))
+}
+
+func mul(x, y *Number) *Number {
+	if isZero(x) || isZero(y) {
+		return zero()
+	}
+	return add(mul(x, sub1(y)), x)
+}
+
+func fact(n *Number) *Number {
+	if isZero(n) {
+		return add1(zero())
+	}
+	return mul(fact(sub1(n)), n)
+}
+
+// -------------------------------------
+// Helpers to generate/count Peano integers
+
+func gen(n int) *Number {
+	if n > 0 {
+		return add1(gen(n - 1))
+	}
+	return zero()
+}
+
+func count(x *Number) int {
+	if isZero(x) {
+		return 0
+	}
+	return count(sub1(x)) + 1
+}
+
+// -------------------------------------
+// Print i! for i in [0,9]
+
+func main() {
+	for i := 0; i <= 9; i++ {
+		f := count(fact(gen(i)))
+		fmt.Println(i, "! =", f)
+	}
+}
diff --git a/go.dev/_content/doc/play/pi.go b/go.dev/_content/doc/play/pi.go
new file mode 100644
index 00000000..f3c3f358
--- /dev/null
+++ b/go.dev/_content/doc/play/pi.go
@@ -0,0 +1,34 @@
+// Concurrent computation of pi.
+// See https://goo.gl/la6Kli.
+//
+// This demonstrates Go's ability to handle
+// large numbers of concurrent processes.
+// It is an unreasonable way to calculate pi.
+package main
+
+import (
+	"fmt"
+	"math"
+)
+
+func main() {
+	fmt.Println(pi(5000))
+}
+
+// pi launches n goroutines to compute an
+// approximation of pi.
+func pi(n int) float64 {
+	ch := make(chan float64)
+	for k := 0; k < n; k++ {
+		go term(ch, float64(k))
+	}
+	f := 0.0
+	for k := 0; k < n; k++ {
+		f += <-ch
+	}
+	return f
+}
+
+func term(ch chan float64, k float64) {
+	ch <- 4 * math.Pow(-1, k) / (2*k + 1)
+}
diff --git a/go.dev/_content/doc/play/sieve.go b/go.dev/_content/doc/play/sieve.go
new file mode 100644
index 00000000..51909345
--- /dev/null
+++ b/go.dev/_content/doc/play/sieve.go
@@ -0,0 +1,36 @@
+// A concurrent prime sieve
+
+package main
+
+import "fmt"
+
+// Send the sequence 2, 3, 4, ... to channel 'ch'.
+func Generate(ch chan<- int) {
+	for i := 2; ; i++ {
+		ch <- i // Send 'i' to channel 'ch'.
+	}
+}
+
+// Copy the values from channel 'in' to channel 'out',
+// removing those divisible by 'prime'.
+func Filter(in <-chan int, out chan<- int, prime int) {
+	for {
+		i := <-in // Receive value from 'in'.
+		if i%prime != 0 {
+			out <- i // Send 'i' to 'out'.
+		}
+	}
+}
+
+// The prime sieve: Daisy-chain Filter processes.
+func main() {
+	ch := make(chan int) // Create a new channel.
+	go Generate(ch)      // Launch Generate goroutine.
+	for i := 0; i < 10; i++ {
+		prime := <-ch
+		fmt.Println(prime)
+		ch1 := make(chan int)
+		go Filter(ch, ch1, prime)
+		ch = ch1
+	}
+}
diff --git a/go.dev/_content/doc/play/solitaire.go b/go.dev/_content/doc/play/solitaire.go
new file mode 100644
index 00000000..15022aa1
--- /dev/null
+++ b/go.dev/_content/doc/play/solitaire.go
@@ -0,0 +1,117 @@
+// This program solves the (English) peg
+// solitaire board game.
+// http://en.wikipedia.org/wiki/Peg_solitaire
+
+package main
+
+import "fmt"
+
+const N = 11 + 1 // length of a row (+1 for \n)
+
+// The board must be surrounded by 2 illegal
+// fields in each direction so that move()
+// doesn't need to check the board boundaries.
+// Periods represent illegal fields,
+// ● are pegs, and ○ are holes.
+
+var board = []rune(
+	`...........
+...........
+....●●●....
+....●●●....
+..●●●●●●●..
+..●●●○●●●..
+..●●●●●●●..
+....●●●....
+....●●●....
+...........
+...........
+`)
+
+// center is the position of the center hole if
+// there is a single one; otherwise it is -1.
+var center int
+
+func init() {
+	n := 0
+	for pos, field := range board {
+		if field == '○' {
+			center = pos
+			n++
+		}
+	}
+	if n != 1 {
+		center = -1 // no single hole
+	}
+}
+
+var moves int // number of times move is called
+
+// move tests if there is a peg at position pos that
+// can jump over another peg in direction dir. If the
+// move is valid, it is executed and move returns true.
+// Otherwise, move returns false.
+func move(pos, dir int) bool {
+	moves++
+	if board[pos] == '●' && board[pos+dir] == '●' && board[pos+2*dir] == '○' {
+		board[pos] = '○'
+		board[pos+dir] = '○'
+		board[pos+2*dir] = '●'
+		return true
+	}
+	return false
+}
+
+// unmove reverts a previously executed valid move.
+func unmove(pos, dir int) {
+	board[pos] = '●'
+	board[pos+dir] = '●'
+	board[pos+2*dir] = '○'
+}
+
+// solve tries to find a sequence of moves such that
+// there is only one peg left at the end; if center is
+// >= 0, that last peg must be in the center position.
+// If a solution is found, solve prints the board after
+// each move in a backward fashion (i.e., the last
+// board position is printed first, all the way back to
+// the starting board position).
+func solve() bool {
+	var last, n int
+	for pos, field := range board {
+		// try each board position
+		if field == '●' {
+			// found a peg
+			for _, dir := range [...]int{-1, -N, +1, +N} {
+				// try each direction
+				if move(pos, dir) {
+					// a valid move was found and executed,
+					// see if this new board has a solution
+					if solve() {
+						unmove(pos, dir)
+						fmt.Println(string(board))
+						return true
+					}
+					unmove(pos, dir)
+				}
+			}
+			last = pos
+			n++
+		}
+	}
+	// tried each possible move
+	if n == 1 && (center < 0 || last == center) {
+		// there's only one peg left
+		fmt.Println(string(board))
+		return true
+	}
+	// no solution found for this board
+	return false
+}
+
+func main() {
+	if !solve() {
+		fmt.Println("no solution found")
+	}
+	fmt.Println(moves, "moves tried")
+}
diff --git a/go.dev/_content/doc/play/tree.go b/go.dev/_content/doc/play/tree.go
new file mode 100644
index 00000000..3790e6cd
--- /dev/null
+++ b/go.dev/_content/doc/play/tree.go
@@ -0,0 +1,100 @@
+// Go's concurrency primitives make it easy to
+// express concurrent concepts, such as
+// this binary tree comparison.
+//
+// Trees may be of different shapes,
+// but have the same contents. For example:
+//
+//        4               6
+//      2   6          4     7
+//     1 3 5 7       2   5
+//                  1 3
+//
+// This program compares a pair of trees by
+// walking each in its own goroutine,
+// sending their contents through a channel
+// to a third goroutine that compares them.
+
+package main
+
+import (
+	"fmt"
+	"math/rand"
+)
+
+// A Tree is a binary tree with integer values.
+type Tree struct {
+	Left  *Tree
+	Value int
+	Right *Tree
+}
+
+// Walk traverses a tree depth-first,
+// sending each Value on a channel.
+func Walk(t *Tree, ch chan int) {
+	if t == nil {
+		return
+	}
+	Walk(t.Left, ch)
+	ch <- t.Value
+	Walk(t.Right, ch)
+}
+
+// Walker launches Walk in a new goroutine,
+// and returns a read-only channel of values.
+func Walker(t *Tree) <-chan int {
+	ch := make(chan int)
+	go func() {
+		Walk(t, ch)
+		close(ch)
+	}()
+	return ch
+}
+
+// Compare reads values from two Walkers
+// that run simultaneously, and returns true
+// if t1 and t2 have the same contents.
+func Compare(t1, t2 *Tree) bool {
+	c1, c2 := Walker(t1), Walker(t2)
+	for {
+		v1, ok1 := <-c1
+		v2, ok2 := <-c2
+		if !ok1 || !ok2 {
+			return ok1 == ok2
+		}
+		if v1 != v2 {
+			break
+		}
+	}
+	return false
+}
+
+// New returns a new, random binary tree
+// holding the values 1k, 2k, ..., nk.
+func New(n, k int) *Tree {
+	var t *Tree
+	for _, v := range rand.Perm(n) {
+		t = insert(t, (1+v)*k)
+	}
+	return t
+}
+
+func insert(t *Tree, v int) *Tree {
+	if t == nil {
+		return &Tree{nil, v, nil}
+	}
+	if v < t.Value {
+		t.Left = insert(t.Left, v)
+		return t
+	}
+	t.Right = insert(t.Right, v)
+	return t
+}
+
+func main() {
+	t1 := New(100, 1)
+	fmt.Println(Compare(t1, New(100, 1)), "Same Contents")
+	fmt.Println(Compare(t1, New(99, 1)), "Differing Sizes")
+	fmt.Println(Compare(t1, New(100, 2)), "Differing Values")
+	fmt.Println(Compare(t1, New(101, 2)), "Dissimilar")
+}