Text Justification

// Java program to justify the given text
// according to the given width of each line

import java.util.ArrayList;
import java.util.List;
public class GFG {

    // function to count the characters from arr[start] to
    // arr[end], both start and end inclusive
    static int countCharacters(int start, int end, 
                               		   List<String> arr) {
        int cnt = 0;
        for (int i = start; i <= end; i++)
            cnt += arr.get(i).length();
        return cnt;
    }

    // function to fill the end of str with spaces
    static String padLine(String str, int W) {
        int len = str.length();
        StringBuilder sb = new StringBuilder(str);
        for (int i = 0; i < W - len; i++)
            sb.append(' ');
        return sb.toString();
    }

    // function to form a line using all the words in range [start, end]
    // and justify the line to push it to the result
    static String justify(int start, int end, List<String> arr, int W) {
        StringBuilder justifiedLine = new StringBuilder();
        int wordsCnt = end - start + 1;

        // If the line has only 1 word, then pad it with spaces and return it
        if (wordsCnt == 1)
            return padLine(arr.get(start), W);

        int spaceCnt = W - countCharacters(start, end, arr);
        String space = " ";
        int extraSpaces = 0;

        // If this line is not the last line, then all the words should
        // have even spaces between them and all the extra spaces will
        // be added to the spaces to the left
        if (end != arr.size() - 1) {
            space = new String(new char[spaceCnt / (wordsCnt - 1)])
              										.replace('\0', ' ');
            extraSpaces = spaceCnt % (wordsCnt - 1);
        }

        for (int i = start; i <= end; i++) {

            // Add the word to the justified line
            justifiedLine.append(arr.get(i));

            // add spaces to the justified line
            justifiedLine.append(space);

            // If there are extra spaces, add it to the spaces to the left
            if (extraSpaces > 0) {
                justifiedLine.append(' ');
                extraSpaces -= 1;
            }
        }

        // Remove extra spaces from the right end
        while (justifiedLine.length() > W)
            justifiedLine.setLength(justifiedLine.length() - 1);

        // Pad line with spaces if we have empty space to the right
        return padLine(justifiedLine.toString(), W);
    }

    // function to get the end index such that all the words from
    // start to end can be placed in one line
    static int getEnd(int start, List<String> arr, int W) {
        int end = start + 1;
        int len = arr.get(start).length();
        while (end < arr.size() && (len + 1 + arr.get(end).length()) <= W) {
            len += arr.get(end).length() + 1;
            end += 1;
        }
        return end - 1;
    }

    // function to combine the words to each line and justify the line
    // from both sides
    static List<String> justifyText(List<String> arr, int W) {
        int start = 0;
        List<String> justifiedText = new ArrayList<>();

        while (start < arr.size()) {

            // find the ending index such that words in the range
            // [start, end] can be put in a single line
            int end = getEnd(start, arr, W);

            // Form a line using words from start to end and justify it
            String justifiedLine = justify(start, end, arr, W);

            // Push the justified line to the result
            justifiedText.add(justifiedLine);
            start = end + 1;
        }
        return justifiedText;
    }

    public static void main(String[] args) {
        List<String> arr = List.of("GfG", "is", "the", "best", 
				"computer", "science", "portal", "for", "geeks." );
        int W = 16;

        List<String> ans = justifyText(arr, W);
        for (String line : ans)
            System.out.println(line);
    }
}