Reverse String

Problem Statement

Write a function that reverses a string. The input string is given as an array of characters s.

You must do this by modifying the input array in-place with minimal extra memory usage.

Method Signature

Java

public static void reverseString(char[] s)

Examples

Example 1:

Input: s = ['h','e','l','l','o']

Output: ['o','l','l','e','h']

Example 2:

Input: s = ['H','a','n','n','a','h']

Output: ['h','a','n','n','a','H']

Example 3:

Input: s = ['A']

Output: ['A']

Explanation: Single character remains unchanged

Example 4:

Input: s = ['a','b']

Output: ['b','a']

Explanation: Two characters swap positions

Test Your Solution

Java

import java.util.Arrays;

public class ReverseStringTest {
    public static void main(String[] args) {
        // Test case 1
        char[] test1 = {'h','e','l','l','o'};
        System.out.println("Before: " + Arrays.toString(test1));
        reverseString(test1);
        System.out.println("After:  " + Arrays.toString(test1)); // Expected: [o, l, l, e, h]

        // Test case 2
        char[] test2 = {'H','a','n','n','a','h'};
        System.out.println("Before: " + Arrays.toString(test2));
        reverseString(test2);
        System.out.println("After:  " + Arrays.toString(test2)); // Expected: [h, a, n, n, a, H]

        // Test case 3 - Single character
        char[] test3 = {'A'};
        System.out.println("Before: " + Arrays.toString(test3));
        reverseString(test3);
        System.out.println("After:  " + Arrays.toString(test3)); // Expected: [A]

        // Test case 4 - Two characters
        char[] test4 = {'a','b'};
        System.out.println("Before: " + Arrays.toString(test4));
        reverseString(test4);
        System.out.println("After:  " + Arrays.toString(test4)); // Expected: [b, a]

        // Test case 5 - Even length
        char[] test5 = {'1','2','3','4'};
        System.out.println("Before: " + Arrays.toString(test5));
        reverseString(test5);
        System.out.println("After:  " + Arrays.toString(test5)); // Expected: [4, 3, 2, 1]
    }

    // Your implementation goes here
    public static void reverseString(char[] s) {
        // TODO: Implement string reversal in-place
    }
}

Extension Challenges

Reverse substring: Reverse only characters from index i to j
Reverse words: Reverse entire string, then reverse each word individually
Reverse with exclusions: Skip certain characters (like spaces or punctuation)
Palindrome check: Modify to check if string reads same forwards and backwards
Rotate array: Use similar two-pointer technique for array rotation

Real-World Applications

Text processing: Reversing user input or display strings
Algorithms: Palindrome detection, string matching
Data structures: Implementing reverse iterators
Cryptography: Simple character scrambling (though not secure)
Game development: Text effects and animations

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