Main.java

import java.io.BufferedReader;
import java.io.FileReader;
import java.io.IOException;
import java.util.ArrayList;
import java.util.List;

/*
@author: mc-es

Problem 42
The nth term of the sequence of triangle numbers is given by Tn=n(n+1)/2; so the first ten triangle numbers are:
 1,3,6,10,15,21,28,36,45,55,...
By converting each letter in a word to a number corresponding to its alphabetical position and adding these values we form a word value.
For example, the word value for SKY is 19+11+25=55=10. If the word value is a triangle number then we shall call the word a triangle word.

Using words.txt (right click and 'Save Link/Target As...'), a 16K text file containing nearly two-thousand common English words, how many are triangle words?

Answer: 162
*/

public class Main {
 public static void main(String[] args) {
 List<String> words = new ArrayList<>();

 try (BufferedReader br = new BufferedReader(new FileReader("words.txt"))) {
 String line = br.readLine();
 if (line != null) {
 line = line.replace("\"", "");
 String[] wordArray = line.split(",");
 for (String word : wordArray) {
 words.add(word);
 }
 }
 } catch (IOException e) {
 System.err.println("Error reading file: " + e.getMessage());
 return;
 }

 int triangleWordCount = 0;
 for (String word : words) {
 if (isTriangleNumber(calculateWordValue(word))) {
 triangleWordCount++;
 }
 }

 System.out.println("Number of triangle words: " + triangleWordCount);
 }

 public static boolean isTriangleNumber(int n) {
 double x = (-1 + Math.sqrt(1 + 8 * n)) / 2;
 return x == (int) x;
 }

 public static int calculateWordValue(String word) {
 int value = 0;
 for (char c : word.toCharArray()) {
 value += c - 'A' + 1;
 }
 return value;
 }
}