String Reversal Approaches in DSA Go - Build from Scratch

String Reversal Approaches

📖 Scenario: Imagine you have a list of words that you want to reverse to see them backwards. This is like reading a word from right to left instead of left to right.

🎯 Goal: You will create a program that reverses a given string using a simple approach. You will first store the string, then prepare a helper variable, then reverse the string, and finally print the reversed string.

📋 What You'll Learn

Create a string variable with a specific value

Create a helper variable to hold the reversed string

Use a for loop to reverse the string character by character

Print the reversed string

💡 Why This Matters

🌍 Real World

Reversing strings is useful in text processing, palindromes checking, and coding puzzles.

💼 Career

Understanding string manipulation is fundamental for software development, data processing, and algorithm design.

1

DATA SETUP: Create the original string

Create a string variable called original and set it to the value "hello".

DSA Go

# Create a string variable called original and set it to "hello"
# Your code here

Hint

Use original := "hello" to create the string variable.

2

CONFIGURATION: Create a helper variable for the reversed string

Create a string variable called reversed and set it to an empty string "".

DSA Go

package main

func main() {
    original := "hello"
    // Create a string variable called reversed and set it to empty string
    // Your code here
}

Hint

Use reversed := "" to create an empty string variable.

3

CORE LOGIC: Reverse the string using a for loop

Use a for loop with variable i starting from len(original) - 1 down to 0. Inside the loop, add the character at original[i] to reversed.

DSA Go

package main

func main() {
    original := "hello"
    reversed := ""
    // Use a for loop to reverse the string
    // Your code here
}

Hint

Use a for loop counting down from the last index to zero and add each character to reversed.

4

OUTPUT: Print the reversed string

Use fmt.Println(reversed) to print the reversed string. Remember to import "fmt" at the top.

DSA Go

package main

import "fmt"

func main() {
    original := "hello"
    reversed := ""
    for i := len(original) - 1; i >= 0; i-- {
        reversed += string(original[i])
    }
    // Print the reversed string
    // Your code here
}

Hint

Use fmt.Println(reversed) to show the reversed string on the screen.

Practice

1. What does the strings.Reverse function do in Go if it existed? (Assume it reverses the string.)

easy

A. It converts the string to uppercase.

B. It returns the input string with characters in reverse order.

C. It removes all vowels from the string.

D. It splits the string into words.

Solution

1. Step 1: Understand the function name and purpose

   The function name Reverse suggests it changes the order of characters.

2. Step 2: Interpret the expected behavior

   Reversing a string means the last character becomes first, and so on.

3. Final Answer:

   It returns the input string with characters in reverse order. -> Option B

4. Quick Check:

   Reverse means flip order [OK]

Hint: Reverse means flip the order of characters [OK]

Common Mistakes:

• Confusing reverse with uppercase conversion
• Thinking reverse removes characters
• Assuming reverse splits words

2. Which of the following Go code snippets correctly reverses a string s?

easy

A. var reversed string
for i := len(s)-1; i >= 0; i-- {
reversed += string(s[i])
}

B. for i := 0; i < len(s); i++ {
reversed += string(s[i])
}

C. reversed := strings.ToUpper(s)

D. reversed := strings.Split(s, " ")

Solution

1. Step 1: Analyze the loop direction

   var reversed string for i := len(s)-1; i >= 0; i-- { reversed += string(s[i]) } loops from the last character to the first, building reversed string.

2. Step 2: Check other options

   for i := 0; i < len(s); i++ { reversed += string(s[i]) } loops forward, so no reversal. reversed := strings.ToUpper(s) changes case, reversed := strings.Split(s, " ") splits words.

3. Final Answer:

   Option A correctly reverses the string. -> Option A

4. Quick Check:

   Loop backward to reverse [OK]

Hint: Loop backward from end to start to reverse [OK]

Common Mistakes:

• Looping forward instead of backward
• Using string functions that don't reverse
• Confusing splitting with reversing

3. What is the output of this Go code?

func main() {
  s := "hello"
  reversed := ""
  for i := len(s) - 1; i >= 0; i-- {
    reversed += string(s[i])
  }
  fmt.Println(reversed)
}

medium

A. olleh

B. hello

C. h

D. error

Solution

1. Step 1: Trace the loop from end to start

   The loop starts at index 4 ('o') and goes to 0 ('h'), appending characters in reverse order.

2. Step 2: Build the reversed string

   Characters appended: 'o', 'l', 'l', 'e', 'h' forming "olleh".

3. Final Answer:

   olleh -> Option A

4. Quick Check:

   Reverse of "hello" is "olleh" [OK]

Hint: Reverse string by appending chars from end to start [OK]

Common Mistakes:

• Reading string forward instead of backward
• Printing original string by mistake
• Expecting error due to string indexing

4. Find the error in this Go code that tries to reverse a string s:

func reverse(s string) string {
  var reversed string
  for i := 0; i <= len(s); i++ {
    reversed += string(s[len(s)-i])
  }
  return reversed
}

medium

A. The function should return reversed as a byte slice.

B. The string concatenation should use +=.

C. The loop condition should be i < len(s), not <=.

D. The loop should start from len(s) and go down to 0.

Solution

1. Step 1: Check loop bounds

   The loop runs from 0 to len(s) inclusive, but string indices go from 0 to len(s)-1.

2. Step 2: Identify out-of-range index

   Accessing s[len(s)-i] when i=0 is s[len(s)], which is out of range and causes runtime error.

3. Final Answer:

   The loop condition should be i < len(s), not <=. -> Option C

4. Quick Check:

   Index must be within 0 to len(s)-1 [OK]

Hint: Loop index must stay inside string length bounds [OK]

Common Mistakes:

• Using <= instead of < in loop condition
• Accessing index len(s) which is invalid
• Confusing string and byte slice types

5. Given a string with Unicode characters like "Go语言", which approach correctly reverses it preserving characters properly in Go?

hard

A. Split string by spaces and reverse the words.

B. Use a byte slice and reverse bytes directly.

C. Use strings.ToUpper and then reverse.

D. Convert string to []rune, reverse the rune slice, then convert back to string.

Solution

1. Step 1: Understand Unicode in Go strings

   Go strings are byte sequences; Unicode characters may be multiple bytes.

2. Step 2: Use rune slice to handle Unicode characters

   Converting to []rune treats each Unicode character as one element, safe to reverse.

3. Step 3: Reverse rune slice and convert back

   Reversing []rune reverses characters correctly, then convert back to string.

4. Final Answer:

   Convert string to []rune, reverse runes, then back to string. -> Option D

5. Quick Check:

   Use runes for Unicode-safe reversal [OK]

Hint: Use []rune to reverse Unicode strings safely [OK]

Common Mistakes:

• Reversing bytes breaks Unicode characters
• Using uppercase conversion instead of reversing
• Reversing words instead of characters