68. Text Justification Leetcode Java

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.

Solution:

Check the length word by word, when the total length is greater than the target L, which means, the previous words can be formed a line. Calculate the total space needed for this line, distribute them evenly between each word, if there are extra spaces left, put them from left to right each in one slot. For the last line, add all the words and then fill the rest of positions with whitespaces.

 public List<String> fullJustify(String[] words, int L) {  
     List<String> res=new ArrayList<String>();  
     if(words==null || words.length==0) return res;  
     int start=0;  
     int tL=0;  
     for(int i=0;i<words.length;i++){  
       if(i!=start) tL++;  
       tL+=words[i].length();  
       if(tL>L){  
         tL=tL-words[i].length()-1;  
         int slot=(i-1-start==0)? 1:i-1-start;  
         int wNum=(i-1-start==0)? L-tL : (L-tL)/slot+1;  
         int extraPosition=start-1+(L-tL)%slot;  
         StringBuilder sb=new StringBuilder();  
         for(int j=start;j<=i-1;j++){  
           sb.append(words[j]);  
           if(start==i-1 || j!=i-1) {  
             for(int k=1;k<=wNum;k++) sb.append(" ");  
           }  
           if(j<=extraPosition) sb.append(" ");  
         }  
         res.add(sb.toString());  
         start=i;  
         tL=words[i].length();  
       }  
     }  
     StringBuilder sb=new StringBuilder();  
     for(int i=start;i<words.length;i++){  
         if(i!=start) sb.append(" ");  
         sb.append(words[i]);  
       }  
     for(int j=1;j<=L-tL;j++) sb.append(" ");  
     res.add(sb.toString());  
     return res;  
   }