68. Text Justification

class Solution {
    public List<String> fullJustify(String[] words, int maxWidth) {
        List<List<String>> col = new ArrayList<>();
        int len = 0;
        List<String> list = new ArrayList<>(), re = new ArrayList<>();
        for(String w : words)
        {
            if(len + w.length() <= maxWidth)
            {
                list.add(w);
                len += w.length() + 1;
            }
            else
            {
                col.add(list);
                list = new ArrayList<>();
                list.add(w);
                len = w.length() + 1;
            }
        }
        col.add(list);
        int size = col.size();
        for(int i = 0; i  < size - 1; i++) re.add(f1(col.get(i), maxWidth));
        re.add(f2(col.get(size - 1), maxWidth));
        return re;
    }

    String f1(List<String> list, int w)
    {
        int size = list.size(), wordLen = 0;
        if(size == 1) return f2(list, w);
        for(String word : list) wordLen += word.length();
        w -= wordLen;
        int numSpaces = size - 1,
            restSpaces = w / numSpaces,
            remain = w % numSpaces;
        String perSpace = "";
        while(restSpaces-- > 0) perSpace += " ";
        StringBuilder sb = new StringBuilder();
        sb.append(list.get(0));
        for(int i = 1; i < size; i++)
        {
            sb.append(perSpace);
            if(remain > 0)
            {
                remain--;
                sb.append(" ");
            }
            sb.append(list.get(i));
        }
        return sb.toString();
    }

    String f2(List<String> list, int w)
    {
        StringBuilder sb = new StringBuilder();
        sb.append(String.join(" ", list));
        while(sb.length() < w) sb.append(" ");
        return sb.toString();
    }
}