59 lines
1.8 KiB
Markdown
59 lines
1.8 KiB
Markdown
## Why are maps used for?
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For example, here is an inefficient program that uses a loop to find an element among millions of elements.
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```go
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millions := []int{/* millions of elements */}
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for _, v := range millions {
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if v == userQuery {
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// do something
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}
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}
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```
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1. Maps allow fast-lookup for map keys in O(1) time *CORRECT*
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2. Maps allow fast-lookup for map keys in O(n) time
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3. Maps allow fast-traversal on map keys in O(1) time
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> **1:** That's right. Maps work in O(1) in average for fast-lookup.
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>
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> **2:** Map doesn't work in O(n) time for key lookup.
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>
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## When should you not use a map?
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1. To find an element through a key
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2. To loop over the map keys *CORRECT*
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3. To add structured data to your program
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> **1:** That is when you use a map.
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>
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> **2:** Right! Looping over map keys happen in O(n) time. So, maps are the worst data structures for key traversing.
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>
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> **3:** Maps don't allow you to add structured data to your program.
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## Which type below cannot be a map key?
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1. map[string]int
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2. []string
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3. []int
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4. []bool
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5. All of them *CORRECT*
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> **5:** Slices, maps, and function values are not comparable. So, they cannot be map keys.
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>
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## Which are the key and element types of the map below?
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```go
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map[string]map[int]bool
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```
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1. Key: string Element: bool
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2. Key: string Element: int
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3. Key: string Element: map[int]
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4. Key: string Element: map[int]bool *CORRECT*
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> **4:** The map contains other maps. The element type of a map can be of any type.
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>
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## What is a map value behind the scenes?
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1. A map header
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2. A pointer to a map header *CORRECT*
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3. Tiny data structure with 3 fields: Pointer, Length and Capacity
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> **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). |