Leetcode - 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.

[分析] 该题算法本身不复杂，考察的是对边界条件的处理。题意把握上主要两点：1）当某行只能放下一个单词时，空格全部放在右边 2）最后一行单词间仅有一个空格，多余空格均放在右边。详细分析参考http://blog.csdn.net/linhuanmars/article/details/24063271

public class Solution {
    public List<String> fullJustify(String[] words, int maxWidth) {
        List<String> result = new ArrayList<String>();
        if (words == null || words.length == 0 || maxWidth < 0)
            return result;
        int count = 0, last = 0;
        for (int i = 0; i < words.length; i++) {
            if (count + words[i].length() + (i - last) > maxWidth) {
                int extraNum = 0, spaceNum = 0;
                if (i - 1 > last) {
                    spaceNum = (maxWidth - count) / (i - 1 - last);
                    extraNum = (maxWidth - count) % (i - 1 - last);
                } 
                StringBuilder avgSpaces = new StringBuilder();
                while (spaceNum > 0) {
                    avgSpaces.append(" ");
                    spaceNum--;
                }
                StringBuilder row = new StringBuilder();
                for (int j = last; j < i - 1; j++) {
                    row.append(words[j]);
                    row.append(avgSpaces.toString());
                    if (extraNum > 0) {
                        row.append(" ");
                        extraNum--;
                    }
                }
                row.append(words[i - 1]);
                for (int j = row.length(); j < maxWidth; j++) {
                    row.append(" ");
                }
                result.add(row.toString());
                count = 0;
                last = i;
            }
            count += words[i].length();
        }
        // deal with the last row which sometimes not processed int the above loop
        StringBuilder row = new StringBuilder();
        for (int i = last; i < words.length; i++) {
            row.append(words[i]);
            if (row.length() < maxWidth)
                row.append(" ");
        }
        while (row.length() < maxWidth)
            row.append(" ");
        result.add(row.toString());
        return result;
    }
}