Text Justification

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.

public class Solution {
    public ArrayList<String> fullJustify(String[] words, int L) {
		// Start typing your Java solution below
		// DO NOT write main() function
		ArrayList<String> res = new ArrayList<String>();
		if (words.length == 0)
			return res;
		int index = 0;
		StringBuilder sb = new StringBuilder();
		while (index < words.length) {
			sb = new StringBuilder();
			int volume = 0; // number of chars this line
			int cur_len = 0;// number of chars plus one space for each word
			int counter = 0;
			int initial = index;
			while (index < words.length && words[index].length() + cur_len <= L) {
				cur_len += (words[index].length() + 1);// at least one space
				volume += words[index].length();
				counter++;
				index++;
			}
			if(index == words.length){// if last line, all words go left
				while(initial < index){
					sb.append(words[initial++]);
					if(sb.length() < L)
						sb.append(" ");// one space per word, if length permits for the last word
				}
				while(sb.length() < L)
					sb.append(" ");// add spaces till end of last line
				res.add(sb.toString());
				break;
			}
			int spaces = L - volume;
			if (counter != 1) {
				int spaces_per_word = spaces / (counter - 1);
				int extra_spaces = spaces % (counter - 1);
				while(initial < index){// no "=", since index points to the next word now
					sb.append(words[initial++]);
					if(--counter == 0)//the last word does not need space
						break;
					if(extra_spaces > 0){
						for(int i = 0; i < spaces_per_word; i++)
							sb.append(" ");
						sb.append(" ");// extra one apace for each word
						extra_spaces--;
					}
					else{
						for(int i = 0; i < spaces_per_word; i++)
							sb.append(" ");
					}
				}
			}
			else{// if only one word this line, all spaces go right
				sb.append(words[initial]);
				for(int i = 0; i < spaces; i++)
					sb.append(" ");
			}
			res.add(sb.toString());
		}
		return res;
	}
}