Java String Manipulation Made Simple

#java #algorithms #api #cloud

String questions are everywhere in coding interviews.

And most of them are built on a few simple patterns:

Two pointers
Character arrays
StringBuilder

Master these, and many problems become easy.

1. Reverse a String

The easiest way:

public static String reverse(String str) {
return new StringBuilder(str).reverse().toString();
}

Manual Reverse

public static String reverseManual(String str) {

char[] arr = str.toCharArray();

int left = 0, right = arr.length - 1;

while (left < right) {

    char temp = arr[left];
    arr[left] = arr[right];
    arr[right] = temp;

    left++;
    right--;
}

return new String(arr);

}

Core Idea

Use two pointers:

one from start
one from end

Swap characters until middle.

2. Check Palindrome

A palindrome reads the same forwards and backwards.

Example:

madam
level
public static boolean isPalindrome(String str) {

int left = 0, right = str.length() - 1;

while (left < right) {
```
if (str.charAt(left) != str.charAt(right))
    return false;

left++;
right--;
```
}

return true;
}

Why Two Pointers Work

Compare:

first ↔ last
second ↔ second-last

If all match:

palindrome confirmed.

3. Remove Duplicate Characters

public static String removeDuplicates(String str) {

Set<Character> seen = new LinkedHashSet<>();

for (char c : str.toCharArray()) {
    seen.add(c);
}

StringBuilder sb = new StringBuilder();

for (char c : seen)
    sb.append(c);

return sb.toString();

}

Why LinkedHashSet?

Because it: