add: map exercises and quiz

22-maps/exercises/01-warm-up/main.go

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+package main
+
+// ---------------------------------------------------------
+// EXERCISE: Warm-up
+//
+//  Create and print the following maps.
+//
+//  1. Phone numbers by last name
+//  2. Product availability by Product ID
+//  3. Multiple phone numbers by last name
+//  4. Shopping basket by Customer ID
+//
+//     Each item in the shopping basket has a Product ID and
+//     quantity. Through the map, you can tell:
+//     "Mr. X has bought Y bananas"
+//
+// ---------------------------------------------------------
+
+func main() {
+	// Hint: Store phone numbers as text
+
+	// #1
+	// Key        : Last name
+	// Element    : Last name
+
+	// #2
+	// Key        : Product ID
+	// Element    : Available / Unavailable
+
+	// #3
+	// Key        : Last name
+	// Element    : Phone numbers
+
+	// #4
+	// Key        : Customer ID
+	// Element Key:
+	//   Key: Product ID Element: Quantity
+}

22-maps/exercises/01-warm-up/solution/main.go

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+// 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"
+
+func main() {
+	var (
+		phones map[string]string
+		// Key        : Last name
+		// Element    : Last name
+
+		// Key        : Product ID
+		// Element    : Available / Unavailable
+		products map[int]bool
+
+		multiPhones map[string][]string
+		// Key        : Last name
+		// Element    : Phone numbers
+
+		basket map[int]map[int]int
+		// Key        : Customer ID
+		// Element Key:
+		//   Key: Product ID Element: Quantity
+	)
+
+	fmt.Printf("phones     : %#v\n", phones)
+	fmt.Printf("products   : %#v\n", products)
+	fmt.Printf("multiPhones: %#v\n", multiPhones)
+	fmt.Printf("basket     : %#v\n", basket)
+}

22-maps/exercises/02-populate/main.go

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+package main
+
+// ---------------------------------------------------------
+// EXERCISE: Populate and Lookup
+//
+//  Add elements to the maps that you've declared in the
+//  first exercise, and try them by looking up for the keys.
+//
+//  Use map literals.
+//
+//  After completing the exercise, remove the data and check
+//  that your program still works.
+//
+//
+//  1. Phone numbers by last name
+//     --------------------------
+//     bowen  202-555-0179
+//     dulin  03.37.77.63.06
+//     greco  03489940240
+//
+//     Print the dulin's phone number.
+//
+//
+//  2. Product availability by Product ID
+//     ----------------
+//     617841573 true
+//     879401371 false
+//     576872813 true
+//
+//     Is Product ID 879401371 available?
+//
+//
+//  3. Multiple phone numbers by last name
+//     ------------------------------------------------------
+//     bowen  [202-555-0179]
+//     dulin  [03.37.77.63.06 03.37.70.50.05 02.20.40.10.04]
+//     greco  [03489940240 03489900120]
+//
+//     What is Greco's second phone number?
+//
+//
+//  4. Shopping basket by Customer ID
+//     -------------------------------
+//     100 [617841573:4 576872813:2]
+//     101 [576872813:5 657473833:20]
+//     102 []
+//
+//     How many of 576872813 the customer 101 is going to buy?
+//                (Product ID)  (Customer ID)
+//
+//
+// EXPECTED OUTPUT
+//
+//   1. Run the solution to see the output
+//   2. Here is the output with empty maps:
+//
+//      dulin's phone number: N/A
+//      Product ID #879401371 is not available
+//      greco's 2nd phone number: N/A
+//      Customer #101 is going to buy 0 from Product ID #576872813.
+//
+// ---------------------------------------------------------
+
+func main() {
+}

22-maps/exercises/02-populate/solution/main.go

@@ -0,0 +1,63 @@
+// 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"
+
+func main() {
+	phones := map[string]string{
+		"bowen": "202-555-0179",
+		"dulin": "03.37.77.63.06",
+		"greco": "03489940240",
+	}
+
+	products := map[int]bool{
+		617841573: true,
+		879401371: false,
+		576872813: true,
+	}
+
+	multiPhones := map[string][]string{
+		"bowen": []string{"202-555-0179"},
+		"dulin": []string{
+			"03.37.77.63.06", "03.37.70.50.05", "02.20.40.10.04",
+		},
+		"greco": []string{"03489940240", "03489900120"},
+	}
+
+	basket := map[int]map[int]int{
+		100: {617841573: 4, 576872813: 2},
+		101: {576872813: 5, 657473833: 20},
+		102: {},
+	}
+
+	// Print dulin's phone number.
+	who, phone := "dulin", "N/A"
+	if v, ok := phones[who]; ok {
+		phone = v
+	}
+	fmt.Printf("%s's phone number: %s\n", who, phone)
+
+	// Is Product ID 879401371 available?
+	id, status := 879401371, "available"
+	if !products[id] {
+		status = "not " + status
+	}
+	fmt.Printf("Product ID #%d is %s\n", id, status)
+
+	// What is Greco's second phone number?
+	who, phone = "greco", "N/A"
+	if phones := multiPhones[who]; len(phones) >= 2 {
+		phone = phones[1]
+	}
+	fmt.Printf("%s's 2nd phone number: %s\n", who, phone)
+
+	// How many of 576872813 the customer 101 is going to buy?
+	cid, pid := 101, 576872813
+	fmt.Printf("Customer #%d is going to buy %d from Product ID #%d.\n", cid, basket[cid][pid], pid)
+}

22-maps/exercises/03-students/main.go

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+package main
+
+// ---------------------------------------------------------
+// EXERCISE: Students
+//
+//  Create a program that returns the students by the given
+//  Hogwarts house name (see the data below).
+//
+//  Print the students sorted by name.
+//
+//  "bobo" doesn't belong to Hogwarts, remove it by using
+//  the delete function.
+//
+//
+// RESTRICTIONS
+//
+//  + Add the following data to your map as is.
+//    Do not sort it manually and do not modify it.
+//
+//  + Slices in the map shouldn't be sorted (changed).
+//    HINT: Copy them.
+//
+//
+// EXPECTED OUTPUT
+//
+//  go run main.go
+//
+//  Please type a Hogwarts house name.
+//
+//
+//  go run main.go bobo
+//
+//  Sorry. I don't know anything about "bobo".
+//
+//
+//  go run main.go hufflepuf
+//
+//  ~~~ hufflepuf students ~~~
+//
+//        + diggory
+//        + helga
+//        + scamander
+//        + wenlock
+//
+// ---------------------------------------------------------
+
+func main() {
+	// House        Student Name
+	// ---------------------------
+	// gryffindor   weasley
+	// gryffindor   hagrid
+	// gryffindor   dumbledore
+	// gryffindor   lupin
+	// hufflepuf    wenlock
+	// hufflepuf    scamander
+	// hufflepuf    helga
+	// hufflepuf    diggory
+	// ravenclaw    flitwick
+	// ravenclaw    bagnold
+	// ravenclaw    wildsmith
+	// ravenclaw    montmorency
+	// slytherin    horace
+	// slytherin    nigellus
+	// slytherin    higgs
+	// slytherin    scorpius
+	// bobo         wizardry
+	// bobo         unwanted
+}

22-maps/exercises/03-students/solution/main.go

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+// 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"
+	"os"
+	"sort"
+)
+
+func main() {
+	houses := map[string][]string{
+		"gryffindor": {"weasley", "hagrid", "dumbledore", "lupin"},
+		"hufflepuf":  {"wenlock", "scamander", "helga", "diggory", "bobo"},
+		"ravenclaw":  {"flitwick", "bagnold", "wildsmith", "montmorency"},
+		"slytherin":  {"horace", "nigellus", "higgs", "bobo", "scorpius"},
+		"bobo":       {"wizardry", "unwanted"},
+	}
+
+	// remove "bobo" house
+	delete(houses, "bobo")
+
+	args := os.Args[1:]
+	if len(args) < 1 {
+		fmt.Println("Please type a Hogwarts house name.")
+		return
+	}
+
+	house, students := args[0], houses[args[0]]
+	if students == nil {
+		fmt.Printf("Sorry. I don't know anything about %q.\n", house)
+		return
+	}
+
+	// only sort the clone
+	clone := append([]string(nil), students...)
+	sort.Strings(clone)
+
+	fmt.Printf("~~~ %s students ~~~\n\n", house)
+	for _, student := range clone {
+		fmt.Printf("\t+ %s\n", student)
+	}
+}

22-maps/exercises/README.md

@@ -1,5 +1,15 @@
-# IDEAS
+# Header
 
-* Retrieve sorted map keys
+What you will learn?
 
-* Roman literals
+1. **[Warm Up](https://github.com/inancgumus/learngo/tree/master/22-maps/exercises/01-warm-up)**
+
+    Create and print the maps.
+
+2. **[Populate and Lookup](https://github.com/inancgumus/learngo/tree/master/22-maps/exercises/02-populate)**
+
+    Add elements to the maps that you've declared in the first exercise, and try them by looking up for the keys.
+
+3. **[Hogwarts Students](https://github.com/inancgumus/learngo/tree/master/22-maps/exercises/03-students)**
+
+    Create a program that returns the students by the given Hogwarts house name.

22-maps/questions/README.md

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+## Why are maps used?
+For example, here is a program that uses a slice to find an element among millions of elements.
+```go
+millions := []int{/* millions of elements */}
+for _, v := range millions {
+    if v == userQuery {
+        // do something
+    }
+}
+```
+1. Maps allow fast-lookup for map keys in O(1) time *CORRECT*
+2. Maps allow fast-lookup for map keys in O(n) time
+3. Maps allow fast-traversal on map keys in O(1) time
+
+> **1:** That's right. Maps work in O(1) in average for fast-lookup.
+>
+> **2:** Map doesn't work in O(n) time for key lookup.
+>
+
+## When shouldn't you use a map?
+1. To find an element through a key
+2. To loop over the map keys *CORRECT*
+3. To add structured data to your program
+
+> **1:** That is when you use a map.
+> 
+> **2:** Right! Looping over map keys happen in O(n) time. So, maps are the worst data structures for key traversing.
+>
+> **3:** Maps don't allow you to add structured data to your program.
+
+
+## Which type below cannot be a map key?
+1. map[string]int
+2. []string
+3. []int
+4. []bool
+5. All of them *CORRECT*
+
+> **5:** Slices, maps, and function values are not comparable. So, they cannot be map keys.
+>
+
+## Which are the following map's key and element types?
+```go
+map[string]map[int]bool
+```
+1. Key: string Element: bool
+2. Key: string Element: int
+3. Key: string Element: map[int]
+4. Key: string Element: map[int]string *CORRECT*
+
+> **4:** The map contains other maps. The element type of a map can be of any type.
+>
+
+## What is a map behind the scenes?
+1. A map header
+2. A pointer to a map header *CORRECT*
+3. Tiny data structure with 3 fields: Pointer, Length and Capacity
+
+> **2**: That's right. Maps are complex data structures. However, each map value is only a pointer to a map header (which is a more complex data structure).