Text Justification

1.找到这一行能放几个单词

2.判断last是不是最后一个词

Given an array of words and a width maxWidth, format the text such that each line has exactly maxWidthcharacters 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 maxWidth 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.

Note:

• A word is defined as a character sequence consisting of non-space characters only.

• Each word's length is guaranteed to be greater than 0 and not exceed maxWidth.

• The input array words contains at least one word.

Example 1:

Input:
words = ["This", "is", "an", "example", "of", "text", "justification."]
maxWidth = 16
Output:
[
   "This    is    an",
   "example  of text",
   "justification.  "
]

Example 2:

Input:
words = ["What","must","be","acknowledgment","shall","be"]
maxWidth = 16
Output:
[
  "What   must   be",
  "acknowledgment  ",
  "shall be        "
]
Explanation: Note that the last line is "shall be    " instead of "shall     be",
             because the last line must be left-justified instead of fully-justified.
             Note that the second line is also left-justified becase it contains only one word.

Example 3:

Input:
words = ["Science","is","what","we","understand","well","enough","to","explain",
         "to","a","computer.","Art","is","everything","else","we","do"]
maxWidth = 20
Output:
[
  "Science  is  what we",
  "understand      well",
  "enough to explain to",
  "a  computer.  Art is",
  "everything  else  we",
  "do                  "
]

时间复杂度 o(n),空间复杂度 o(n)

class Solution {
    public List<String> fullJustify(String[] words, int maxWidth) {
        
        List<String> res = new ArrayList<>();
        
        if(words == null || words.length == 0)
            return res;
        
        
        int index = 0;
        
        
        while(index < words.length){
            
            int countLen = words[index].length();
            int last = index+1;
            
            //找到一行能放几个词，循环后 last指在放在下一行的第一个词
            while(last < words.length){
                if(countLen + words[last].length() + 1 > maxWidth){
                   break;
                }
                countLen += 1+words[last].length();
                last++;
            }
            
            //开始组词
            StringBuilder builder = new StringBuilder();
            builder.append(words[index]);
            
            //计算单词之间的空儿，不是空格
            int diff = last - index - 1;
            //判断尾端情况
            
            if(last == words.length || diff == 0){
                for(int i = index + 1; i < last;i++){
                    builder.append(" ");
                    builder.append(words[i]);
                }
                
                for(int i = builder.length();i < maxWidth;i++){
                    builder.append(" ");
                }
            }else{
                int space = (maxWidth - countLen)/diff;
                int r = (maxWidth - countLen)%diff;
                
                for(int i = index + 1; i <last ;i++){
                    for(int j = space; j >0; j--){
                        builder.append(" ");
                    }
                    
                    if(r > 0){
                        builder.append(" ");
                        r--;
                    }
                    builder.append(" ");//因为countLen的时候算了一个空格,和这里要对应
                    builder.append(words[i]);
                }
                
            }
            
            res.add(builder.toString());
            
            index = last;
            
        }
         
        return res;
        
    }
}