Hey I have three questions with creating these methods, thanks.
Write a Function
You will be given one of the following problems to solve using and writing Java functions.
1.
Given a list of words, return an array which indicates the frequency that each letter occurs. For example, in the list [”apple”, ”bob”], [ ’a’ -> 1, ’b’->2, ’e’->1, ’l’->1, ’o’->, ’p’->2] . The order of the array does not matter and a Frequency class will be provided.
2.
Given a list of words, indicate whether the list constitutes a ”Word Lad- der.” A Word Ladder is a series of words where each succeeding word changes by only one letter. You may not assume that all words will be of the same length, and you may not assume the length of the list.
3.
Given an integer greater than 2, X, return an array populated with all prime numbers up to and including X.
1.
Check with your teacher if the list is supposed to be case sensitive. From the context of the question, it should not be.
In this case, convert all the strings into lowercase and compare using the String.toLowerCase() method before comparison.
The comparison can be done character by character using the String.charAt(i) method.
Use an array of size 26 to store the frequencies. Do not forget to initialize the array (or the Frequency class values).
Read the Java API for more details.
http://java.sun.com/javase/6/docs/api/
or to download the API to your computer:
http://java.sun.com/javase/downloads/index.jsp#docs
2.
First compare the lengths of the successive words using String.length().
If they equal, then compare letter by letter, and count the number of different letters. If the difference equals 1, continue the "ladder".
You may have to convert all letters to lowercase before the comparison.
3. There are plenty of algorithms for finding prime numbers. One of them is to test the divisibility by primes. You will have to create a list of primes, starting with 2, which is assumed to be a prime. Test all odd numbers starting from 3. Whenever you find that the number does not divide by the numbers on your prime list, you have found a prime, and add it to your prime list.
For example 3 does not divide by 2, so add 3 to the prime list. 5 does not divide by 2 and 3, add it to the prime list. Likewise, 7 is added to the prime list. 9 divides by 3, so skip it.
11 does not divide by 2,3... so it is a prime.
You do not have to test all the primes on the prime list. If the square of the prime on the prime list exceeds the number X to be tested, X can be declared a prime. For example, for 11, it is not divisible by 2,3, but 5²>11, so 11 can be declared a prime.
It may sound complicated, if you post your pseudocode or the Java code, you can get further help.
Sure, I can help you with your questions! Let's go through each question and explain how to create the respective methods in Java.
1. **Frequency of Letters in a List of Words:**
To solve this problem, you need to write a function that takes a list of words as input and returns an array indicating the frequency of each letter in the words. Here's how you can approach it:
- Create a HashMap<Character, Integer> to store the frequency of each letter.
- Iterate through each word in the list:
- Iterate through each character in the word:
- If the character is already present in the HashMap, increment its value by 1.
- Otherwise, add the character to the HashMap with a value of 1.
- Create an array of Frequency objects with the size of the HashMap.
- Iterate through the HashMap and populate the Frequency objects accordingly.
Here's a code snippet to illustrate the implementation:
```java
import java.util.*;
class Frequency {
char letter;
int frequency;
public Frequency(char letter, int frequency) {
this.letter = letter;
this.frequency = frequency;
}
}
public class Main {
public static Frequency[] getLetterFrequency(List<String> words) {
Map<Character, Integer> frequencyMap = new HashMap<>();
for (String word : words) {
for (char c : word.toCharArray()) {
frequencyMap.put(c, frequencyMap.getOrDefault(c, 0) + 1);
}
}
Frequency[] frequencies = new Frequency[frequencyMap.size()];
int index = 0;
for (Map.Entry<Character, Integer> entry : frequencyMap.entrySet()) {
frequencies[index++] = new Frequency(entry.getKey(), entry.getValue());
}
return frequencies;
}
public static void main(String[] args) {
List<String> words = Arrays.asList("apple", "bob");
Frequency[] frequencies = getLetterFrequency(words);
for (Frequency frequency : frequencies) {
System.out.println(frequency.letter + " -> " + frequency.frequency);
}
}
}
```
2. **Word Ladder Check:**
To check if a list of words constitutes a "Word Ladder," you need to write a function that takes a list of words as input and returns a boolean value indicating if the list meets the given conditions. Here's how you can approach it:
- Start by checking if the list is empty or contains only one word. If yes, then return true.
- Iterate through the words starting from the second word:
- Compare each word with the previous word:
- Count the number of different characters between the two words.
- If the count exceeds 1, return false.
- If the loop completes without returning false, return true.
Here's a code snippet to illustrate the implementation:
```java
import java.util.*;
public class Main {
public static boolean isWordLadder(List<String> words) {
if (words.isEmpty() || words.size() == 1) {
return true;
}
for (int i = 1; i < words.size(); i++) {
String currentWord = words.get(i);
String previousWord = words.get(i - 1);
int diffCount = 0;
if (currentWord.length() != previousWord.length()) {
return false;
}
for (int j = 0; j < currentWord.length(); j++) {
if (currentWord.charAt(j) != previousWord.charAt(j)) {
diffCount++;
}
if (diffCount > 1) {
return false;
}
}
}
return true;
}
public static void main(String[] args) {
List<String> words = Arrays.asList("cat", "cot", "dot", "dog");
boolean isLadder = isWordLadder(words);
System.out.println(isLadder ? "Word Ladder" : "Not a Word Ladder");
}
}
```
3. **Prime Numbers up to X:**
To find all prime numbers up to a given integer X, you need to write a function that takes X as input and returns an array populated with all prime numbers up to and including X. Here's how you can approach it:
- Create an ArrayList<Integer> to store the prime numbers.
- Iterate from 2 to X and for each number:
- Check if it is prime by testing divisibility with all numbers from 2 to its square root.
- If it is not divisible by any number, add it to the ArrayList.
- Convert the ArrayList to an array and return it.
Here's a code snippet to illustrate the implementation:
```java
import java.util.*;
public class Main {
public static boolean isPrime(int num) {
if (num < 2) {
return false;
}
for (int i = 2; i <= Math.sqrt(num); i++) {
if (num % i == 0) {
return false;
}
}
return true;
}
public static int[] getPrimeNumbers(int x) {
List<Integer> primes = new ArrayList<>();
for (int i = 2; i <= x; i++) {
if (isPrime(i)) {
primes.add(i);
}
}
int[] primeArray = new int[primes.size()];
for (int i = 0; i < primes.size(); i++) {
primeArray[i] = primes.get(i);
}
return primeArray;
}
public static void main(String[] args) {
int x = 20;
int[] primeNumbers = getPrimeNumbers(x);
System.out.println(Arrays.toString(primeNumbers));
}
}
```
I hope this helps you in solving your tasks! Let me know if you have any further questions.