Reverse a String

📌 Definition:

📖 Detailed Explanation:

Convert the string to a character array (or iterate from the last index) and swap from both ends toward the middle, or build the result backwards. Strings are immutable in Java, so you cannot mutate the original in place. The two-pointer swap is O(n) time and O(n) space.

💻 Solutions:

• Java
• JavaScript
• Python

public static String reverse(String s) {
    char[] c = s.toCharArray();
    int i = 0, j = c.length - 1;
    while (i < j) {
        char t = c[i]; c[i++] = c[j]; c[j--] = t;
    }
    return new String(c);
}

function reverse(s) {
  return s.split('').reverse().join('');
}
// manual: let out=''; for (let i=s.length-1;i>=0;i--) out+=s[i];

def reverse(s):
    return s[::-1]

# manual: return ''.join(reversed(s))

🔑 Key Points:

• Strings are immutable — build a new value
• Two-pointer swap is O(n) time
• Know the one-liners per language
• Handle null/empty defensively

🌍 Real-World Example: