[Author: @mdimamhosen Date: 2025-04-19 Category: interview-qa/maps Tags: [go, maps, data-structure] ]

Maps

Maps are a data structure which allow us to store data values in key:value pairs. A map is an unordered and changeable collection that does not allow duplicates. The default value of a map is nil.

userInfo := map[string]int{
    "huxn": 17,
    "alex": 18,
    "john": 27,
}

fmt.Println(userInfo)
userInfo["jordan"] = 15
fmt.Println(userInfo["huxn"])
fmt.Println(userInfo["alex"])
fmt.Println(userInfo["john"])

Frequently Asked Questions

1. How do you create a map in Go?

Answer: You can create a map using the make function or by using a map literal.

Code Example:

// Using make function
userInfo := make(map[string]int)
userInfo["huxn"] = 17
userInfo["alex"] = 18
fmt.Println(userInfo)

// Using map literal
userInfo := map[string]int{
    "huxn": 17,
    "alex": 18,
}
fmt.Println(userInfo)

2. How do you check if a key exists in a map?

Answer: You can use the second return value of a map lookup to check if a key exists.

Code Example:

userInfo := map[string]int{
    "huxn": 17,
    "alex": 18,
}

value, exists := userInfo["huxn"]
if exists {
    fmt.Println("Key exists with value:", value)
} else {
    fmt.Println("Key does not exist")
}

3. How do you delete a key from a map?

Answer: You can use the delete function to remove a key from a map.

Code Example:

userInfo := map[string]int{
    "huxn": 17,
    "alex": 18,
}
delete(userInfo, "huxn")
fmt.Println(userInfo)

4. Can a map key be of any type?

Answer: No, map keys must be of a type that is comparable (e.g., strings, integers, etc.).

Code Example:

// Valid keys
userInfo := map[string]int{
    "huxn": 17,
    "alex": 18,
}

// Invalid keys (e.g., slices)
// userInfo := map[[]int]int{} // This will throw an error

5. How do you iterate over a map?

Answer: You can use a for loop with the range keyword to iterate over a map.

Code Example:

userInfo := map[string]int{
    "huxn": 17,
    "alex": 18,
}

for key, value := range userInfo {
    fmt.Printf("Key: %s, Value: %d\n", key, value)
}

6. What is the zero value of a map?

Answer: The zero value of a map is nil.

Code Example:

var userInfo map[string]int
fmt.Println(userInfo == nil) // true

7. Can you compare two maps in Go?

Answer: No, maps cannot be compared directly. You need to compare them manually by iterating over their keys and values.

Code Example:

map1 := map[string]int{"huxn": 17, "alex": 18}
map2 := map[string]int{"huxn": 17, "alex": 18}

// Direct comparison is not allowed
// fmt.Println(map1 == map2) // This will throw an error

// Manual comparison
areEqual := true
for key, value := range map1 {
    if map2[key] != value {
        areEqual = false
        break
    }
}
fmt.Println("Maps are equal:", areEqual)

8. How do you find the length of a map?

Answer: You can use the len function to find the number of key-value pairs in a map.

Code Example:

userInfo := map[string]int{
    "huxn": 17,
    "alex": 18,
}
fmt.Println("Length of map:", len(userInfo))

9. Can you nest maps in Go?

Answer: Yes, you can create a map where the value is another map.

Code Example:

nestedMap := map[string]map[string]int{
    "group1": {
        "huxn": 17,
        "alex": 18,
    },
    "group2": {
        "john": 27,
    },
}
fmt.Println(nestedMap)

10. How do you copy a map in Go?

Answer: You need to manually copy the key-value pairs from one map to another.

Code Example:

originalMap := map[string]int{
    "huxn": 17,
    "alex": 18,
}
copiedMap := make(map[string]int)

for key, value := range originalMap {
    copiedMap[key] = value
}
fmt.Println("Original Map:", originalMap)
fmt.Println("Copied Map:", copiedMap)