Map use cases in Go - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Map key existence check output

What is the output of this Go program that checks if a key exists in a map?

Go

package main
import "fmt"
func main() {
    m := map[string]int{"apple": 5, "banana": 3}
    val, ok := m["orange"]
    fmt.Println(val, ok)
}

A 3 true

B 0 true

C 0 false

D Compilation error

💡 Hint

Check what happens when you access a map with a key that does not exist.

In Go, when you access a map with a key that does not exist, the zero value of the value type is returned (0 for int) and the boolean 'ok' is false.

❓ Predict Output

intermediate

Map iteration order output

What is the output of this Go program that iterates over a map?

Go

package main
import "fmt"
func main() {
    m := map[int]string{1: "one", 2: "two", 3: "three"}
    for k, v := range m {
        fmt.Printf("%d:%s ", k, v)
    }
}

A 1:one 2:two 3:three

B The output order is random and may vary each run

C 3:three 2:two 1:one

D Compilation error

💡 Hint

Remember how Go handles map iteration order.

Go does not guarantee the order of map iteration. The output order can change each time the program runs.

🔧 Debug

advanced

Identify the runtime error in map access

What runtime error will this Go program produce when run?

Go

package main
func main() {
    var m map[string]int
    m["key"] = 10
}

A panic: index out of range

B Compilation error: map not initialized

C No error, program runs fine

D panic: assignment to entry in nil map

💡 Hint

Think about what happens if you assign to a nil map.

Maps must be initialized before assigning values. Assigning to a nil map causes a runtime panic.

🧠 Conceptual

advanced

Map key type restrictions

Which of the following types can be used as keys in Go maps?

A Structs with only comparable fields

B Arrays

C Slices

D Maps

💡 Hint

Map keys must be comparable types in Go.

Go map keys must be types that can be compared with '=='. Slices and maps are not comparable, arrays and structs are if their fields are comparable.

🚀 Application

expert

Count word frequency using a map

What is the final value of the map after running this Go program that counts word frequency?

Go

package main
import (
    "fmt"
    "strings"
)
func main() {
    text := "go go gophers go"
    words := strings.Fields(text)
    freq := make(map[string]int)
    for _, w := range words {
        freq[w]++
    }
    fmt.Println(freq)
}

A map[go:3 gophers:1]

B map[go:4 gophers:1]

C map[go:3 gophers:0]

D map[go:2 gophers:1]

💡 Hint

Count how many times 'go' appears in the text.

The word 'go' appears 3 times and 'gophers' once. The map counts each word's frequency correctly.