add: bouncing ball exercise #3

18-bouncing-ball-project/exercises/03-single-dimensional/main.go

@@ -0,0 +1,121 @@
+// For more tutorials: https://blog.learngoprogramming.com
+//
+// Copyright © 2018 Inanc Gumus
+// Learn Go Programming Course
+// License: https://creativecommons.org/licenses/by-nc-sa/4.0/
+//
+
+package main
+
+import (
+	"fmt"
+	"time"
+
+	"github.com/inancgumus/screen"
+	"github.com/mattn/go-runewidth"
+)
+
+// ---------------------------------------------------------
+// EXERCISE: Single Dimensional
+//
+//  In this exercise you will understand why I use
+//  a multi-dimensional board slice instead of a
+//  single-dimensional one.
+//
+//  1. Remove this:
+//     board := make([][]bool, width)
+//
+//  2. Use this:
+//     board := make([]bool, width*height)
+//
+//  3. Adjust the rest of the operations in the code to work
+//     with this single-dimensional slice.
+//
+//     You'll see how hard it becomes to work with it.
+//
+// ---------------------------------------------------------
+
+func main() {
+	const (
+		cellEmpty = ' '
+		cellBall  = '⚾'
+
+		maxFrames = 1200
+		speed     = time.Second / 20
+	)
+
+	var (
+		px, py   int    // ball position
+		ppx, ppy int    // previous ball position
+		vx, vy   = 5, 2 // velocities
+
+		cell rune // current cell (for caching)
+	)
+
+	// you can get the width and height using the screen package easily:
+	width, height := screen.Size()
+
+	// get the rune width of the ball emoji
+	ballWidth := runewidth.RuneWidth(cellBall)
+
+	// adjust the width and height
+	width /= ballWidth
+	height-- // there is a 1 pixel border in my terminal
+
+	// create the board
+	board := make([][]bool, width)
+	for row := range board {
+		board[row] = make([]bool, height)
+	}
+
+	// create a drawing buffer
+	buf := make([]rune, 0, width*height)
+
+	// clear the screen once
+	screen.Clear()
+
+	for i := 0; i < maxFrames; i++ {
+		// calculate the next ball position
+		px += vx
+		py += vy
+
+		// when the ball hits a border reverse its direction
+		if px <= 0 || px >= width-1 {
+			vx *= -1
+		}
+		if py <= 0 || py >= height-1 {
+			vy *= -1
+		}
+
+		// check whether the ball goes beyond the borders
+		if px < width && py < height {
+			// remove the previous ball and put the new ball
+			board[px][py], board[ppx][ppy] = true, false
+
+			// save the previous positions
+			ppx, ppy = px, py
+		}
+
+		// rewind the buffer (allow appending from the beginning)
+		buf = buf[:0]
+
+		// draw the board into the buffer
+		for y := range board[0] {
+			for x := range board {
+				cell = cellEmpty
+				if board[x][y] {
+					cell = cellBall
+				}
+				buf = append(buf, cell, ' ')
+			}
+			buf = append(buf, '\n')
+		}
+
+		// print the buffer
+		screen.MoveTopLeft()
+		fmt.Print(string(buf))
+
+		// slow down the animation
+		time.Sleep(speed)
+	}
+}

18-bouncing-ball-project/exercises/03-single-dimensional/solution/main.go

@@ -0,0 +1,104 @@
+// For more tutorials: https://blog.learngoprogramming.com
+//
+// Copyright © 2018 Inanc Gumus
+// Learn Go Programming Course
+// License: https://creativecommons.org/licenses/by-nc-sa/4.0/
+//
+
+package main
+
+import (
+	"fmt"
+	"time"
+
+	"github.com/inancgumus/screen"
+	"github.com/mattn/go-runewidth"
+)
+
+func main() {
+	const (
+		cellEmpty = ' '
+		cellBall  = '⚾'
+
+		maxFrames = 1200
+		speed     = time.Second / 20
+	)
+
+	var (
+		px, py   int    // ball position
+		ppx, ppy int    // previous ball position
+		vx, vy   = 5, 2 // velocities
+
+		cell rune // current cell (for caching)
+	)
+
+	// you can get the width and height using the screen package easily:
+	width, height := screen.Size()
+
+	// get the rune width of the ball emoji
+	ballWidth := runewidth.RuneWidth(cellBall)
+
+	// adjust the width and height
+	width /= ballWidth
+	height-- // there is a 1 pixel border in my terminal
+
+	// create a single-dimensional board
+	board := make([]bool, width*height)
+
+	// create a drawing buffer
+	buf := make([]rune, 0, width*height)
+
+	// clear the screen once
+	screen.Clear()
+
+	for i := 0; i < maxFrames; i++ {
+		// calculate the next ball position
+		px += vx
+		py += vy
+
+		// when the ball hits a border reverse its direction
+		if px <= 0 || px >= width-1 {
+			vx *= -1
+		}
+		if py <= 0 || py >= height-1 {
+			vy *= -1
+		}
+
+		// check whether the ball goes beyond the borders
+		if px < width && py < height {
+			// calculate the new and the previous ball positions
+			pos := py*width + px
+			ppos := ppy*width + ppx
+
+			// remove the previous ball and put the new ball
+			board[pos], board[ppos] = true, false
+
+			// save the previous positions
+			ppx, ppy = px, py
+		}
+
+		// rewind the buffer (allow appending from the beginning)
+		buf = buf[:0]
+
+		// draw the board into the buffer
+		for y := 0; y < height; y++ {
+			for x := 0; x < width; x++ {
+				cell = cellEmpty
+
+				if board[y*width+x] {
+					cell = cellBall
+				}
+
+				buf = append(buf, cell, ' ')
+			}
+			buf = append(buf, '\n')
+		}
+
+		// print the buffer
+		screen.MoveTopLeft()
+		fmt.Print(string(buf))
+
+		// slow down the animation
+		time.Sleep(speed)
+	}
+}

18-bouncing-ball-project/exercises/README.md

@@ -8,3 +8,6 @@
 
     Let's optimize the program once more. This time you're going to optimize the clearing off the previous positions.
 
+3. **[Use a single dimensional slice]()**
+
+    For the board slice, instead of using a multi-dimensional slice, let's use a single-dimensional slice. In this exercise, you'll understand and deeply internalize why I've used a multi-dimensional board slice.