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.

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

Solution：

思路：
Time Complexity: O(N) Space Complexity: O(N)

Solution Code：

public class Solution {
    public List<String> fullJustify(String[] words, int L) {
        List<String> result = new ArrayList<String>();
        
        int index = 0;
        while (index < words.length) {
            // find how many words can fit in this line, stored in last(index)
            int count = words[index].length();
            int last = index + 1;
            while (last < words.length) {
                if (words[last].length() + count + 1 > L) break;
                count += words[last].length() + 1;
                last++;
            }


            // copy words to stringbuilder for this line according to [last]
            StringBuilder builder = new StringBuilder();
            int index_diff = last - index - 1; // words number
            // if last line or number of words in the line is 1, left-justified
            if (last == words.length || index_diff == 0) {
                for (int i = index; i < last; i++) {
                    builder.append(words[i] + " ");
                }
                builder.deleteCharAt(builder.length() - 1);
                for (int i = builder.length(); i < L; i++) {
                    builder.append(" ");
                }
            } else {
                // middle justified
                // L - count: total spaces
                // index_diff: words number
                int spaces = (L - count) / index_diff;
                int extra = (L - count) % index_diff;
                for (int i = index; i < last; i++) {
                    builder.append(words[i]);
                    if (i < last - 1) {
                        // ((i - index) < extra ? 1 : 0, for different i, assign extra more spaces(not even)
                        for (int j = 0; j <= (spaces + ((i - index) < extra ? 1 : 0)); j++) {
                            builder.append(" ");
                        }
                    }
                }
            }
            result.add(builder.toString());

            index = last;
        }
        
        
        return result;
    }
}