68. 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 exactlyL 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.

首先决定每一行能够容纳的单词数，每两个单词之间至少需要有一个空格，如果空间不足只能推到下一行。

维护一个sum数组用于表示可选单词的长度累加，例如上面的sum[]={4，6，8，15，17，21，35}，设置lastindex，用于指示上一次选到单词组的末尾单词位置。尽量寻找不找过每行长度限制的单词数目，sum[k]-(lastlindex==-1?0:sum[lastlindex])+k-lastlindex-1 用于选择每一行的单词数目，

k-lastlindex-1 的含义是如果每个单词都间隔最小即用一个空格来隔开，需要多少个空格。

找到了一个可以放置在一行的单词组以后对空格进行处理，将空格平均分配，遇到不能平均分配的时候例如maxWidth=16，单词组总长=8，总共需要补8个空格，可以设置一个数组用于表示空格个数，8/3=2 ，将数组置为{2,2,2}，8%3=2，将数组前两个元素+1 即分配好了空格。

最后一行的格式特别，单独处理，另外如果每行只有一个单词，就将单词左对齐，右边补空格直至maxWidth

public static List<String> fullJustify(String[] words, int maxWidth){int len=words.length;int lastlindex=-1;int[] sum=new int[len];int cal=0;List<String> retlist=new ArrayList<>();for(int i=0;i<len;i++){cal+=words[i].length();sum[i]=cal;}while(lastlindex<len){int k=lastlindex+1;for(;k<len&&sum[k]-(lastlindex==-1?0:sum[lastlindex])+k-lastlindex-1<=maxWidth;k++);k--;int count=k-lastlindex;StringBuilder sb=new StringBuilder();if(count==0)break;if(k==len-1){sb.append(words[lastlindex+1]);for(int m=0;m<count-1;m++){sb.append(" ");sb.append(words[lastlindex+2+m]);}for(int m=sb.length();m<maxWidth;m++)sb.append(" ");}else if(count==1){sb.append(words[lastlindex+1]);for(int m=words[lastlindex+1].length();m<maxWidth;m++)sb.append(" ");}else{int totalsize=sum[k]-(lastlindex==-1?0:sum[lastlindex]);int[] blacksize=new int[count-1];int av=(maxWidth-totalsize)/(count-1);Arrays.fill(blacksize, av);int mod=(maxWidth-totalsize)%(count-1);for(int m=0;m<mod;m++)blacksize[m]++;sb.append(words[lastlindex+1]);for(int m=0;m<count-1;m++){for(int f=0;f<blacksize[m];f++)sb.append(" ");sb.append(words[lastlindex+2+m]);}}lastlindex=k;retlist.add(sb.toString());}return retlist;}