Text Justification

By | August 17, 2014

Question

Given an array of words and a length L, format the text such that each line has exactly L characters and is fully (left and right) justified.
You should pack your words in a greedy approach; that is, pack as many words as you can in each line. Pad extra spaces ‘ ‘ when necessary so that each line has exactly L characters.
Extra spaces between words should be distributed as evenly as possible. If the number of spaces on a line do not divide evenly between words, the empty slots on the left will be assigned more spaces than the slots on the right.
For the last line of text, it should be left justified and no extra space is inserted between words.

For example,

words: ["This", "is", "an", "example", "of", "text", "justification."]
L: 16.

Return the formatted lines as:

[
   "This    is    an",
   "example  of text",
   "justification.  "
]

Note: Each word is guaranteed not to exceed Lin length.

Corner Cases:

A line other than the last line might contain only one word. What should you do in this case?
In this case, that line should be left-justified.

My Solution

  public List<String> fullJustify(String[] words, int L) {
    if (words == null || words.length == 0) {
      return Collections.emptyList();
    }
    List<Line> lines = parseToLines(words, L);
    return fillLines(lines, L);
  }

  private List<String> fillLines(List<Line> lines, int L) {
    List<String> output = new ArrayList<String>();
    for (int i = 0; i < lines.size(); i++) {
      Line line = lines.get(i);
      if (line.wordCount() == 1) {
        StringBuilder sb = new StringBuilder();
        sb.append(line.words.get(0));
        sb.append(getSlot(L - line.totalNonSpaceLetterLength()));
        output.add(sb.toString());
      } else if (i == lines.size() - 1) {
        StringBuilder sb = new StringBuilder();
        sb.append(line.words.get(0));
        for (int j = 1; j < line.wordCount(); j++) {
          sb.append(' ');
          sb.append(line.words.get(j));
        }
        sb.append(getSlot(L - line.minimumLength()));
        output.add(sb.toString());
      } else {
        int space = (L - line.totalNonSpaceLetterLength())
            / (line.wordCount() - 1);
        int remain = (L - line.totalNonSpaceLetterLength())
            % (line.wordCount() - 1);
        StringBuilder sb = new StringBuilder();
        sb.append(line.words.get(0));
        for (int j = 1; j <= remain; j++) {
          sb.append(getSlot(space+1));
          sb.append(line.words.get(j));
        }
        for (int j = remain+1; j < line.wordCount(); j++) {
          sb.append(getSlot(space));
          sb.append(line.words.get(j));
        }
        output.add(sb.toString());
      }
    }
    return output;
  }

  private String getSlot(int i) {
    char[] cs = new char[i];
    Arrays.fill(cs, ' ');
    return new String(cs);
  }

  private List<Line> parseToLines(String[] words, int L) {
    List<Line> lines = new ArrayList<Line>();
    Line currentLine = new Line();
    lines.add(currentLine);
    for (String word : words) {
      if (currentLine.minimumLength() + word.length() < L) {
        currentLine.addWord(word);
      } else {
        currentLine = new Line();
        lines.add(currentLine);
        currentLine.addWord(word);
      }
    }
    return lines;
  }

  class Line {

    private List<String> words;
    private int totalLength;

    Line() {
      words = new ArrayList<String>();
      totalLength = 0;
    }

    void addWord(String word) {
      words.add(word);
      totalLength += word.length();
    }

    int wordCount() {
      return words.size();
    }

    int totalNonSpaceLetterLength() {
      return totalLength;
    }

    int minimumLength() {
      return totalLength + words.size() - 1;
    }
  }

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