refactor: slice exercises 16-21

16-slices/exercises/16-internals-backing-array-fix/main.go

@@ -9,25 +9,19 @@ package main
 
 import (
 	"fmt"
-	"math/rand"
-	"time"
 )
 
 // ---------------------------------------------------------
 // EXERCISE: Fix the backing array problem
 //
-//  You receive numbers from an API. After you're done working
-//  with it, the API needs to continue using those numbers.
-//
-//  But your program changes the numbers (changes the API's slice).
-//
-//  Fix the program so that your program doesn't modify
-//  the original numbers.
+//  Ensure that changing the elements of the `mine` slice
+//  does not change the elements of the `nums` slice.
 //
 //
-// RESTRICTION
+// CURRENT OUTPUT (INCORRECT)
 //
-//  Fix the problem only in the designated area of the code below.
+//  Mine         : [-50 -100 -150 25 30 50]
+//  Original nums: [-50 -100 -150]
 //
 //
 // EXPECTED OUTPUT
@@ -35,26 +29,27 @@ import (
 //  Mine         : [-50 -100 -150]
 //  Original nums: [56 89 15]
 //
-//  Note: Original nums may vary (they're random)
-//        But your slice should look like the above (mine slice)
-//
-//        Yes, it should output only three numbers for the both slices!
-//
 // ---------------------------------------------------------
 
 func main() {
-	// API returns random numbers in an int slice
-	rand.Seed(time.Now().UnixNano())
-	nums := rand.Perm(100)
+	// DON'T TOUCH THE FOLLOWING CODE
+	nums := []int{56, 89, 15, 25, 30, 50}
 
 	// ----------------------------------------
-	// RESTRICTIONS — ONLY ADD YOUR CODE HERE
+	// ONLY ADD YOUR CODE HERE
 	//
+	// Ensure that nums slice never changes even though
+	// the mine slice changes.
 	mine := nums
-	//
 	// ----------------------------------------
 
+	// DON'T TOUCH THE FOLLOWING CODE
+	//
+	// This code changes the elements of the nums
+	// slice.
+	//
 	mine[0], mine[1], mine[2] = -50, -100, -150
-	fmt.Println("Mine         :", mine)
+
+	fmt.Println("Mine         :", mine[:3])
 	fmt.Println("Original nums:", nums[:3])
 }

16-slices/exercises/16-internals-backing-array-fix/solution/main.go

@@ -9,13 +9,10 @@ package main
 
 import (
 	"fmt"
-	"math/rand"
-	"time"
 )
 
 func main() {
-	rand.Seed(time.Now().UnixNano())
-	nums := rand.Perm(100)
+	nums := []int{56, 89, 15, 25, 30, 50}
 
 	// ----------------------------------------
 	// breaks the connection:

16-slices/exercises/17-internals-backing-array-sort/main.go

@@ -16,12 +16,12 @@ import (
 //
 //  1. Sort only the middle 3 items.
 //
-//  2. All the slices should see your change.
+//  2. All the slices should see your changes.
 //
 //
 // RESTRICTION
 //
-//  Do not sort manually. Sort by slicing then by using the sort package.
+//  Do not sort manually. Sort by using the sort package.
 //
 //
 // EXPECTED OUTPUT

16-slices/exercises/18-internals-slice-header/main.go

@@ -20,9 +20,9 @@ import (
 //
 // EXPECTED OUTPUT
 //
-//  Note that, your memory usage numbers may vary. These are on my
-//  own system. However, the size of the arrays and slices should be
-//  the same on your own system as well (if you're on 64-bit machine).
+//  Note that, your memory usage numbers may vary. However, the size of the
+//  arrays and slices should be the same on your own system as well
+//  (if you're on a 64-bit machine).
 //
 //
 //  [initial memory usage]
@@ -54,62 +54,73 @@ import (
 //    - Just call it with a message that matches to the expected output.
 //
 //    passArray function:
-//    - Accepts a [size]int array, so you can pass it your array.
 //    - It automatically prints the memory usage.
+//    - Accepts a [size]int array, so you can pass your array to it.
 //
 //    passSlice function:
-//    - Accepts an int slice, so you can pass it one of your slices.
 //    - It automatically prints the memory usage.
+//    - Accepts an int slice, so you can pass it one of your slices.
 //
 // ---------------------------------------------------------
 
 const size = 1e7
 
 func main() {
-	// stops the gc: prevents cleaning up the memory
+	// don't worry about this code.
+	// it stops the garbage collector: prevents cleaning up the memory.
+	// see the link if you're curious:
+	// https://en.wikipedia.org/wiki/Garbage_collection_(computer_science)
 	debug.SetGCPercent(-1)
 
-	// run the program to see what this prints
+	// run the program to see the initial memory usage.
 	report("initial memory usage")
 
 	// 1. allocate an array with 10 million int elements
-	//    this array's size is equal to ~80MB
-	//    hint: use the `size` constant
-	//
-	// 2. print the memory usage
+	//    the array's size will be equal to ~80MB
+	//    hint: use the `size` constant above.
+
+	// 2. print the memory usage (use the report func).
+
+	// 3. copy the array to a new array.
 
-	// 3. copy the array to a new array (just assign)
 	// 4. print the memory usage
 
 	// 5. pass the array to the passArray function
 
-	// 6. convert the one of the arrays to a slice (by slicing)
+	// 6. convert one of the arrays to a slice
+
 	// 7. slice only the first 1000 elements of the array
+
 	// 8. slice only the elements of the array between 1000 and 10000
-	// 9. print the memory usage
+
+	// 9. print the memory usage (report func)
 
 	// 10. pass the one of the slices to the passSlice function
 
 	// 11. print the sizes of the arrays and slices
 	//     hint: use the unsafe.Sizeof function
+	//     see more here: https://golang.org/pkg/unsafe/#Sizeof
 }
 
-// observe that passing an array affects the memory usage dramatically
-//
 // passes [size]int array — about 80MB!
+//
+// observe that passing an array to a function (or assigning it to a variable)
+// affects the memory usage dramatically
 func passArray(items [size]int) {
 	items[0] = 100
 	report("inside passArray")
 }
 
-// observe that passing a slice doesn't affect the memory usage
-//
 // only passes 24-bytes of slice header
+//
+// observe that passing a slice doesn't affect the memory usage
 func passSlice(items []int) {
 	items[0] = 100
 	report("inside passSlice")
 }
 
+// reports the current memory usage
+// don't worry about this code
 func report(msg string) {
 	var m runtime.MemStats
 	runtime.ReadMemStats(&m)

16-slices/exercises/18-internals-slice-header/solution/main.go

@@ -17,7 +17,6 @@ import (
 const size = 1e7
 
 func main() {
-	// stops the gc: prevents cleaning up the memory
 	debug.SetGCPercent(-1)
 
 	report("initial memory usage")

16-slices/exercises/19-observe-len-cap/main.go

@@ -27,7 +27,7 @@ func main() {
 	//
 	// 7. comment out everything
 	//
-	// 8. declare it again using a slice literal
+	// 8. declare the games slice again using a slice literal
 	//    (use the same elements from step 3)
 
 	// --- #2 ---

16-slices/exercises/21-correct-the-lyric/main.go

@@ -34,7 +34,7 @@ import (
 //
 // BONUS
 //
-//   + Think about when does the append allocates a new backing array.
+//   + Think about when does the append allocate a new backing array.
 //
 //   + Check whether your conclusions are correct.
 //

16-slices/exercises/23-limit-the-backing-array-sharing/main.go

@@ -32,6 +32,19 @@ import (
 //  `api.temps` slice.
 //
 //
+// BE CAREFUL
+//
+//   This code imports the api package from the learn go programming
+//   original repository. So, when you change the code in the api folder
+//   ensure that this code imports your own code.
+//
+//   see above (this is the original repository code):
+//   you need to change it to your own repository if you're using your own
+//   repository:
+//
+//   "github.com/inancgumus/learngo/16-slices/exercises/23-limit-the-backing-array-sharing/api"
+//
+//
 // STEPS
 //
 //   You only need to change the code inside the `api/api.go` folder

16-slices/exercises/25-add-lines/main.go

@@ -55,6 +55,7 @@ import (
 //
 //   go get -u github.com/inancgumus/prettyslice
 //
+//
 // ---------------------------------------------------------
 
 func main() {

16-slices/exercises/README.md

@@ -80,11 +80,11 @@ Please update your local copy of the prettyslice package for some examples to wo
 
 2. **[Limit the backing array sharing](https://github.com/inancgumus/learngo/tree/master/16-slices/exercises/23-limit-the-backing-array-sharing)**
 
-    Your API does not control the slices that it share with the outside world. You need to fix it.
+    Your package needs to control the slices that it shares with the outside world.
 
 3. **[Fix the Memory Leak](https://github.com/inancgumus/learngo/tree/master/16-slices/exercises/24-fix-the-memory-leak)**
 
-    A slice retrieved from an API causes a memory leak in your program. You need to fix it.
+    A slice retrieved from a package causes a memory leak in your program. You need to fix it.
 
 4. **[Add a newline after each sentence](https://github.com/inancgumus/learngo/tree/master/16-slices/exercises/25-add-lines)**
 
@@ -92,4 +92,4 @@ Please update your local copy of the prettyslice package for some examples to wo
 
 5. **[Print Daily Requests](https://github.com/inancgumus/learngo/tree/master/16-slices/exercises/26-print-daily-requests)**
 
-    Group the requests log into a multi-dimensional from a single-dimensional slice. Allocate a slice with the exact size needed by doing some wizardary calculations. And lastly, pretty print the result.
+    Group the web request logs into a multi-dimensional slice. Allocate a slice with the exact size needed by doing some wizardary calculations. And lastly, pretty print the result.