Map creation in Go - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output of this Go map creation code?

Consider the following Go code snippet that creates and initializes a map. What will be printed when this program runs?

Go

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

A Compilation error

B 8

C 0

D 53

💡 Hint

Remember that map values can be accessed by their keys and you can add integers.

The map has two keys: "apple" with value 5 and "banana" with value 3. Adding these values results in 8.

❓ Predict Output

intermediate

What is the length of the map after this code runs?

Look at this Go code that creates a map and adds elements. What is the length of the map after execution?

Go

package main
import "fmt"
func main() {
    m := make(map[int]string)
    m[1] = "one"
    m[2] = "two"
    m[1] = "uno"
    fmt.Println(len(m))
}

A 2

B 3

C 1

D 0

💡 Hint

Maps cannot have duplicate keys; adding a key again updates the value.

The map has keys 1 and 2. The key 1 is updated, not added again, so length is 2.

❓ Predict Output

advanced

What error does this Go code produce?

This Go code tries to create a map with a nil key. What error will it produce when compiled or run?

Go

package main
func main() {
    m := make(map[*int]string)
    var p *int = nil
    m[p] = "nil pointer"
}

A panic: runtime error: hash of nil pointer

B Compilation error: invalid map key type

C panic: assignment to entry in nil map

D No error, map accepts nil pointer as key

💡 Hint

In Go, nil pointers can be used as map keys if the key type is a pointer.

Go allows nil pointers as map keys if the key type is a pointer. No error occurs.

❓ Predict Output

advanced

What is the output of this Go map creation with composite literals?

What will this Go program print when run?

Go

package main
import "fmt"
func main() {
    m := map[string][]int{
        "a": {1, 2},
        "b": {3, 4},
    }
    m["a"] = append(m["a"], 5)
    fmt.Println(m["a"])
}

A [1 2 5]

B [1 2]

C [5]

D Compilation error: cannot use composite literal

💡 Hint

Appending to a slice inside a map updates the slice stored at that key.

The slice at key "a" is initially [1, 2]. Appending 5 results in [1, 2, 5].

🧠 Conceptual

expert

Which option correctly creates a map with keys of type struct and values of type int?

You want to create a Go map where keys are structs with two int fields and values are integers. Which option correctly declares and initializes this map with one entry where the struct has fields 1 and 2, and the value is 10?

A m := map[struct{x, y int}]int{{1, 2}: 10}

B m := map[struct{x int; y int}]int{struct{x int; y int}{1, 2}: 10}

C m := map[struct{x int; y int}]int{{x: 1, y: 2}: 10}

D }01 :}2 :y ,1 :x{{tni]}tni y ;tni x{tcurts[pam =: m

💡 Hint

Struct field declarations in Go use semicolons or newlines, not commas, and composite literals can use field names.

Option C correctly uses semicolons in struct type and field names in composite literal. Option C misses types, B is verbose but valid syntax but uses redundant struct type in key, D uses comma instead of semicolon causing syntax error.