Text Justification

TextJustification.java

/**
 * 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 L in 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.
 */

public class Solution {
    public ArrayList<String> fullJustify(String[] words, int L) {
        int wordsCount = words.length;
        ArrayList<String> res = new ArrayList<String>();
        int curLen = 0;
        int lastI = 0;
        for(int i = 0; i <= wordsCount; i++) {
            if(i == wordsCount || curLen + words[i].length() + i - lastI > L) {
                StringBuffer buf = new StringBuffer();
                int spaceCount = L - curLen;
                int spaceSlots = i - lastI - 1;
                if (spaceSlots == 0 || i == wordsCount) {
                    for (int j = lastI; j < i; j++) {
                        buf.append(words[j]);
                        if (j != i - 1) {
                            appendSpace(buf, 1); 
                        }
                    }
                    // append spaces at the end of line. 
                    appendSpace(buf, L - buf.length());
                } else {
                    int spaceEach = spaceCount / spaceSlots;
                    int spaceExtra = spaceCount % spaceSlots;
                    for(int j = lastI; j < i; j++) {
                        buf.append(words[j]);
                        if(j != i - 1)
                            appendSpace(buf, spaceEach + (j - lastI < spaceExtra ? 1 : 0));
                    }
                }
                res.add(buf.toString()); 
                lastI = i;
                curLen = 0;
            }
            if (i < wordsCount) 
                curLen += words[i].length();
        }
        return res;
    }
    private void appendSpace(StringBuffer sb, int count) {
        for(int i = 0; i < count; i++) {
            sb.append(' ');
        }
    }
}