learngo/22-maps/questions

Why are maps used for?

For example, here is an inefficient program that uses a loop to find an element among millions of elements.

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 should you not 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 key and element types of the map below?

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]bool CORRECT

4: The map contains other maps. The element type of a map can be of any type.

What is a map value 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).