Solution.java

class Solution {
    public List<String> fullJustify(String[] words, int maxWidth) {
        ArrayList<String> res = new ArrayList<>();
        if (words == null || words.length == 0) return res;
        int count = 0, last = 0;
        for (int i = 0; i < words.length; i++) {
            if (count + words[i].length() + (i - last) > maxWidth) {
                int spaceNum = 0, extraNum = 0;
                if (i - last - 1 > 0) {
                    spaceNum = (maxWidth - count) / (i - last - 1);
                    extraNum = (maxWidth - count) % (i - last - 1);
                }
                StringBuilder str = new StringBuilder();
                for (int j = last; j < i; j++) {
                    str.append(words[j]);
                    if (j < i - 1) {
                        for (int k = 0; k < spaceNum; k++) str.append(" ");
                        if (extraNum > 0) str.append(" ");
                        extraNum--;
                    }
                }
                for (int j = str.length(); j < maxWidth; j++) str.append(" ");
                res.add(str.toString());
                count = 0;
                last = i;
            }
            count += words[i].length();
        }
        StringBuilder str = new StringBuilder();
        for (int i = last; i < words.length; i++) {
            str.append(words[i]);
            if (str.length() < maxWidth) str.append(" ");
        }
        for (int i = str.length(); i < maxWidth; i++) str.append(" ");
        res.add(str.toString());
        return res;
    }
}