Code Implementation
Message Encryption Implementation
Below is the implementation of the message encryption:
1234567891011121314151617181920212223242526272829303132function reverseString(s) { // Convert string to array (strings are immutable in JavaScript) const chars = s.split(''); // Two pointers approach let left = 0; let right = chars.length - 1; while (left < right) { // Swap characters const temp = chars[left]; chars[left] = chars[right]; chars[right] = temp; // Move pointers towards the middle left++; right--; } // Convert array back to string return chars.join('');} // Alternative approach using built-in methodsfunction reverseStringAlt(s) { return s.split('').reverse().join('');} // Test casesconsole.log(reverseString("hello")); // "olleh"console.log(reverseString("Secure Message")); // "egasseM eruceS"console.log(reverseString("Agent 007")); // "700 tnegA"Step-by-Step Explanation
Let's break down the implementation:
- Initialize Pointers: Set up two pointers: one at the beginning of the string (left) and one at the end (right).
- Swap Characters: Swap the characters at the left and right positions using a temporary variable.
- Move Pointers: Increment the left pointer and decrement the right pointer to move them toward the center.
- Repeat Until Done: Continue swapping and moving pointers until they meet or cross each other.
- Return Result: Return the modified string, which is now reversed.
String Problems
Learning Objective
Implement the message encryption solution in different programming languages.
Message Encryption Implementation
Below is the implementation of the message encryption in different programming languages. Select a language tab to view the corresponding code.
1234567891011121314151617181920212223242526272829303132function reverseString(s) { // Convert string to array (strings are immutable in JavaScript) const chars = s.split(''); // Two pointers approach let left = 0; let right = chars.length - 1; while (left < right) { // Swap characters const temp = chars[left]; chars[left] = chars[right]; chars[right] = temp; // Move pointers towards the middle left++; right--; } // Convert array back to string return chars.join('');} // Alternative approach using built-in methodsfunction reverseStringAlt(s) { return s.split('').reverse().join('');} // Test casesconsole.log(reverseString("hello")); // "olleh"console.log(reverseString("Secure Message")); // "egasseM eruceS"console.log(reverseString("Agent 007")); // "700 tnegA"Step-by-Step Explanation
1Initialize Pointers
Set up two pointers: one at the beginning of the string (left) and one at the end (right).
2Swap Characters
Swap the characters at the left and right positions using a temporary variable.
3Move Pointers
Increment the left pointer and decrement the right pointer to move them toward the center.
4Repeat Until Done
Continue swapping and moving pointers until they meet or cross each other.
5Return Result
Return the modified string, which is now reversed.
Language-Specific Notes
JavaScript
- Strings are immutable, so we convert to an array first
- Uses
split('')to convert string to array - Uses
join('')to convert array back to string - Alternative:
split('').reverse().join('')
Python
- Strings are immutable, so we convert to a list first
- Uses
list(s)to convert string to list - Uses
''.join(chars)to convert list back to string - Python allows tuple unpacking for elegant swapping:
a, b = b, a - Alternative:
s[::-1](slice notation)
Java
- Strings are immutable, so we convert to a char array
- Uses
toCharArray()to convert string to char array - Creates a new String from the char array
- Alternative:
new StringBuilder(s).reverse().toString()
C++
- Strings are mutable in C++, so we can modify directly
- Uses standard indexing for character access
- Alternative:
std::reverse(s.begin(), s.end())from<algorithm>
Key Takeaways
- The two pointers technique is an efficient way to reverse a string in-place.
- For languages with immutable strings, we need to convert to a mutable data structure first.
- Built-in reverse functions are convenient but may use more memory.
- The time complexity is O(n) for both approaches, but the space complexity can differ.
- This algorithm is a fundamental building block for more complex string manipulation problems.
Try It Yourself
Modify the code to implement an alternative approach and test it with the same examples.
Challenge:
Implement a function that solves the message encryption problem using a different approach than shown above.
Common Edge Cases
Empty String
An empty string reversed is still an empty string.
Single Character
A string with a single character remains unchanged when reversed.
Palindrome
A palindrome reads the same forward and backward, so reversing has no effect.