This article consists of Commonly asked Java String coding problems and their solutions.
1) How do you reverse a String in Java using all possible ways?
We can reverse a string in many possible ways. The three most popular approaches are listed below.
a) By Using String Buffer
In Java, StringBuffer is a class representing a mutable sequence of characters. This is synchronized and thread-safe hence suitable for string modification.
public class ReverseString {
public static void main(String[] args) {
StringReverse("automationqahub");
}
public static void StringReverse(String str) {
StringBuffer bf = new StringBuffer(str);
System.out.println(bf.reverse());
}
}b) Converting String to a character array.
In Java, a Character Array is a data structure used to store sequences of characters.
public class ReverseString {
public static void main(String[] args) {
StringReverse("automationqahub");
}
public static void StringReverse(String str) {
char ar[] = str.toCharArray();
for (int i = str.length() - 1; i >= 0; i--) {
System.out.print(ar[i]);
}}}c) By Using Recursion
Recursion in Java is a technique that allows a function to call itself within the body of its own function.
public class ReverseString {
public static void main(String[] args) {
StringReverseusingRecursion("automationqahub");
}
public static void StringReverseusingRecursion(String str) {
if ((str == null) || (str.length() <= 1))
System.out.println(str);
else {
System.out.print(str.charAt(str.length() - 1));
StringReverseusingRecursion(str.substring(0, str.length() - 1));
}
}
}2) Write a Java program to reverse words in a String by preserving spaces.
Input: hello world
Output: olleh dlrowCode:
class ReverseString {
public static void main(String[] args) {
String str = "hello world";
String[] words = str.split(" ");
String reversedString = "";
for (int i = 0; i < words.length; i++) {
String word = words[i];
for (int j = word.length() - 1; j >= 0; j--) {
reversedString += word.charAt(j);
}
reversedString += " ";
}
System.out.println(reversedString);
}
}3) Write a Java Program to check if String is Panagram or not.
Panagram String: A string is a Panagram String if it contains every letter of the alphabet at least once. Panagram strings must include every letter from A to Z and are usually case-insensitive.
Input: "The quick brown fox jumps over the lazy dog."
Output: The input string is a pangram import java.util.HashSet;
class PanagramChecking {
public static void main(String[] args) {
String input = "The quick brown fox jumps over the lazy dog";
HashSet<Character> hs = new HashSet<Character>();
for (int i = 0; i < input.length(); i++) {
char c = input.charAt(i);
if ((c >= 'a' && c <= 'z') || (c >= 'A' && c <= 'Z')) {
hs.add(Character.toLowerCase(c)); // to avoid case-sensitivity issues
}
}
System.out.println("Unique alphabetic characters: " + hs.size());
if (hs.size() == 26) {
System.out.println("The input string is a pangram.");
} else {
System.out.println("The input string is not a pangram.");
}
}
}4) Write a Program in Java to find the longest common prefix among all Strings present in the array.
Input: arr[] = {"avenge","avengers","avent","avb"};
Output: avCode_1:
This code checks for each subsequent string if the current prefix is a prefix of the string. If not, reduce the prefix by one character, check again and continue until the current prefix is a prefix of all strings or it becomes empty.
public class LongestCommonPrefix {
public static void main(String[] args) {
String[] strs = {"avenge","avengers","avent","avb"};
System.out.println(longestCommonPrefix(strs));
}
public static String longestCommonPrefix(String[] strs) {
if (strs == null || strs.length == 0) return "";
String prefix = strs[0];
for (int i = 1; i < strs.length; i++) {
while (strs[i].indexOf(prefix) != 0) {
prefix = prefix.substring(0, prefix.length() - 1);
if (prefix.isEmpty()) return "false";
}
}
return prefix;
}
}
Code_2:
The code below finds the longest common prefix by sorting the array of strings, comparing the first and last strings (which are the most different in a sorted array), and building the prefix character by character.
import java.util.Arrays;
public class LongestCommonPrefix {
public static String longestCommonPrefix(String[] strs) {
StringBuilder result = new StringBuilder();
// Sort the array
Arrays.sort(strs);
// Get the first and last strings
char[] first = strs[0].toCharArray();
char[] last = strs[strs.length - 1].toCharArray();
// Start comparing
for (int i = 0; i < first.length; i++) {
if (first[i] != last[i])
break;
result.append(first[i]);
}
return result.toString();
}
public static void main(String[] args) {
String[] strs = {"avenge","avengers","avent","avb"};
System.out.println(longestCommonPrefix(strs));
}
}5) Given a list of words followed by two words, the task is to find the minimum distance between the given two words in the list of words.
Input: S = { "the", "quick", "brown", "fox", "quick"}
word1 = "the"
word2 = "fox"
Output: 3Code:
class FindClosestString {
public static void main(String[] args) {
String arr[] = {"java", "for", "geeks", "contribute", "practice"};
String word1="geeks";
String word2 ="practice";
int index1=0;
int index2=0;
for(int i=0;i<arr.length-1;i++)
{
if(arr[i]==word1)
{
index1 =i;
}
if(arr[i]==word2)
{
index2=i;
}
}
System.out.println("distance is:"+Math.abs(index2-index1));
}
}6) Write a Java program to find if two Strings are Anagram or not.
Anagram String: Anagram strings are strings that can be transformed into each other by rearranging their characters. Example: “listen” and “silent” or “evil” and “vile”.
Code:
import java.util.Arrays;
public class AnagramCheck {
public static boolean areAnagrams(String str1, String str2) {
// Remove all white spaces and convert to lowercase
str1 = str1.replaceAll("\\s", "").toLowerCase();
str2 = str2.replaceAll("\\s", "").toLowerCase();
if (str1.length() != str2.length()) {
return false;
}
char[] charArray1 = str1.toCharArray();
char[] charArray2 = str2.toCharArray();
// Sort the char arrays
Arrays.sort(charArray1);
Arrays.sort(charArray2);
return Arrays.equals(charArray1, charArray2);
}
public static void main(String[] args) {
String str1 = "listen";
String str2 = "silent";
if (areAnagrams(str1, str2)) {
System.out.println(str1 + " and " + str2 + " are anagrams.");
} else {
System.out.println(str1 + " and " + str2 + " are not anagrams.");
}
}
}
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