Character Frequency Counting in DSA Go - Interactive Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to initialize an empty map to count character frequencies.

DSA Go

freq := map[rune]int[1]

Drag options to blanks, or click blank then click option'

A<>

B[]

C()

D{}

Attempts:

3 left

💡 Hint

Common Mistakes

Using square brackets [] instead of curly braces {}

Using parentheses () which are for function calls

Using angle brackets <> which are not valid in Go

In Go, to create an empty map, use the map literal `map[rune]int{}`.

2fill in blank

medium

Complete the code to loop over each character in the string 'text'.

DSA Go

for _, ch := [1] text {

Drag options to blanks, or click blank then click option'

Arange

Bof

Con

Dover

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'of' which is not valid in Go

Using 'on' or 'over' which are not Go keywords

In Go, to loop over elements in a string or slice, use 'for _, value := range collection'.

3fill in blank

hard

Fix the error in the code to increment the frequency count of character 'ch'.

DSA Go

freq[ch] [1] freq[ch] + 1

Drag options to blanks, or click blank then click option'

A==

B=

C+=

D:=

Attempts:

3 left

💡 Hint

Common Mistakes

Using '==' which is a comparison operator

Using '+=' which is invalid for map elements

Using ':=' which declares a new variable

To update a map value, assign the new value with '='. '+=' does not work directly on map elements.

4fill in blank

hard

Fill both blanks to print each character and its frequency from the map.

DSA Go

for ch, count := [1] freq {
    fmt.[2]("%c: %d\n", ch, count)
}

Drag options to blanks, or click blank then click option'

Arange

BPrintln

CPrintf

DPrint

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'Println' which does not support format specifiers

Using 'Print' which prints without formatting

Using 'for ch, count := freq' which is invalid syntax

Use 'range' to iterate over map keys and values. Use 'Printf' to format output with characters and numbers.

5fill in blank

hard

Fill all three blanks to create a map of character frequencies from a string 'input'.

DSA Go

func charFreq(input string) map[rune]int {
    freq := map[rune]int[1]
    for _, ch := [2] input {
        freq[ch] [3] freq[ch] + 1
    }
    return freq
}

Drag options to blanks, or click blank then click option'

A{}

Brange

C=

Dof

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'of' instead of 'range' in the loop

Using '+=' instead of '=' for map assignment

Not initializing the map properly

Initialize map with '{}', loop with 'range', and assign increment with '='.

Practice

1. What does character frequency counting in a string help us find?

easy

A. How many times each character appears in the string

B. The length of the string

C. The first character of the string

D. The position of a character in the string

Solution

1. Step 1: Understand character frequency counting

   It means counting how many times each character shows up in a string.

2. Step 2: Compare with other options

   Length, first character, or position are different concepts, not frequency counting.

3. Final Answer:

   How many times each character appears in the string -> Option A

4. Quick Check:

   Frequency counting = count characters [OK]

Hint: Frequency means count of each character [OK]

Common Mistakes:

• Confusing frequency with string length
• Thinking frequency means position
• Mixing frequency with substring extraction

2. Which Go code snippet correctly initializes a map to count character frequencies?

easy

A. freq := make(map[rune]int)

B. freq := map[int]string{}

C. freq := []int{}

D. freq := make([]rune, 0)

Solution

1. Step 1: Identify correct map initialization for character counts

   We need a map with keys as characters (rune) and values as counts (int), so make(map[rune]int) is correct.

2. Step 2: Check other options

   freq := map[int]string{} uses wrong types (int keys, string values), C and D are slices, not maps.

3. Final Answer:

   freq := make(map[rune]int) -> Option A

4. Quick Check:

   Map for rune to int = freq map [OK]

Hint: Use map[rune]int for char frequency in Go [OK]

Common Mistakes:

• Using slice instead of map
• Wrong key or value types in map
• Not using make() for map initialization

3. What is the output of this Go code?

package main
import "fmt"
func main() {
  s := "hello"
  freq := make(map[rune]int)
  for _, ch := range s {
    freq[ch]++
  }
  fmt.Println(freq['l'])
}

medium

A. 3

B. 1

C. 2

D. 0

Solution

1. Step 1: Count occurrences of 'l' in "hello"

   The string "hello" has 'l' twice (positions 2 and 3).

2. Step 2: Check map frequency for 'l'

   freq['l'] increments twice, so freq['l'] = 2.

3. Final Answer:

   2 -> Option C

4. Quick Check:

   Count of 'l' in "hello" = 2 [OK]

Hint: Count repeated chars carefully [OK]

Common Mistakes:

• Counting only once
• Confusing index with count
• Using wrong character in print

4. Find the error in this Go code for counting character frequency:

package main
import "fmt"
func main() {
  s := "test"
  freq := map[rune]int{}
  for i := 0; i < len(s); i++ {
    freq[s[i]] += 1
  }
  fmt.Println(freq)
}

medium

A. fmt.Println cannot print maps

B. Map freq is not initialized properly

C. Loop should use range instead of index

D. Using s[i] as byte instead of rune causes wrong map key type

Solution

1. Step 1: Check map key type and s[i] type

   Map keys are rune but s[i] is byte, causing type mismatch.

2. Step 2: Understand why this is an error

   Go does not automatically convert byte to rune for map keys, so this causes a compile error.

3. Final Answer:

   Using s[i] as byte instead of rune causes wrong map key type -> Option D

4. Quick Check:

   Byte vs rune key mismatch error [OK]

Hint: Use rune(s[i]) or range loop for correct key type [OK]

Common Mistakes:

• Ignoring byte vs rune difference
• Assuming map auto-converts keys
• Thinking map initialization is wrong

5. Given a string, how can you find the character with the highest frequency using Go maps?

hard

A. Use a slice to store counts and pick the last element

B. Count frequencies in a map, then iterate map to find max count character

C. Sort the string and pick the first character

D. Print the string length as the highest frequency

Solution

1. Step 1: Count character frequencies using a map

   Use a map[rune]int to count how many times each character appears.

2. Step 2: Iterate the map to find the character with the highest count

   Loop through the map keys and values, track the max count and corresponding character.

3. Final Answer:

   Count frequencies in a map, then iterate map to find max count character -> Option B

4. Quick Check:

   Map count + max search = highest frequency char [OK]

Hint: Use map to count, then find max by iteration [OK]

Common Mistakes:

• Sorting string does not give frequency
• Using slice without mapping chars
• Confusing length with frequency