Deleting map entries in Go - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output after deleting a key from a map?

Consider the following Go code that deletes a key from a map. What will be printed?

Go

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

A map[a:1 b:2 c:3]

B map[]

C map[b:2]

D map[a:1 c:3]

💡 Hint

Deleting a key removes it from the map, so it won't appear in the output.

The delete function removes the key "b" from the map. So the map only contains keys "a" and "c" after deletion.

❓ Predict Output

intermediate

What happens when deleting a non-existent key?

What will be the output of this Go program?

Go

package main
import "fmt"
func main() {
    m := map[int]string{1: "one", 2: "two"}
    delete(m, 3)
    fmt.Println(m)
}

A map[]

B map[3:]

C map[1:one 2:two]

D runtime error

💡 Hint

Deleting a key that does not exist does not cause an error.

Deleting a non-existent key does nothing. The map remains unchanged.

🔧 Debug

advanced

Why does this code cause a runtime panic?

This Go code tries to delete a key from a map but causes a runtime panic. What is the cause?

Go

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

A The map m is nil and cannot be used with delete.

B The key "key" does not exist in the map.

C The delete function requires a pointer to the map.

D The map must be initialized with make before deleting.

💡 Hint

Check if the map is initialized before using delete.

A nil map cannot be used with delete; it causes a runtime panic.

❓ Predict Output

advanced

How many entries remain after deleting keys in a loop?

What is the length of the map after deleting keys in this Go code?

Go

package main
import "fmt"
func main() {
    m := map[int]int{1:10, 2:20, 3:30, 4:40}
    for k := range m {
        if k%2 == 0 {
            delete(m, k)
        }
    }
    fmt.Println(len(m))
}

A 2

B 4

C 0

D 3

💡 Hint

Keys 2 and 4 are even and get deleted.

Keys 2 and 4 are deleted, leaving keys 1 and 3, so length is 2.

🧠 Conceptual

expert

What is the behavior of deleting keys during map iteration?

In Go, what is the guaranteed behavior when deleting keys from a map while iterating over it?

A Deleting keys during iteration is safe and the iteration will skip deleted keys.

B The iteration order is undefined and deleting keys may cause some keys to be skipped or visited twice.

C Deleting keys during iteration causes a runtime panic.

D The map is copied before iteration, so deleting keys does not affect the iteration.

💡 Hint

Map iteration order is random and deleting keys affects iteration unpredictably.

Go's map iteration order is random and deleting keys during iteration can cause keys to be skipped or visited multiple times. This behavior is not guaranteed to be consistent.