34行到36行这里看不明白,为什么要这么写啊

感觉这样写的话,每行第一个单词前面会有空格,但没有所以看不懂了

class Solution {
    public List<String> fullJustify(String[] words, int maxWidth) {
        List<String> ans = new ArrayList<>();
        int right = 0, n =words.length;
        while(true){
            int left = right;
            int sumLen = 0;

            while(right<n && sumLen + words[right].length() + right -left <=maxWidth){
                sumLen += words[right++].length();
            }

            if(right == n){
                StringBuffer sb = join(words,left,n," ");
                sb.append(blank(maxWidth - sb.length()));
                ans.add(sb.toString());
                return ans;

            }

            int numWords = right - left;
            int numSpaces = maxWidth - sumLen;

            if(numWords == 1){
                StringBuffer sb = new StringBuffer(words[left]);
                sb.append(blank(numSpaces));
                ans.add(sb.toString());
                continue;
            }

            int avgSpaces = numSpaces/(numWords-1);
            int extraSpaces = numSpaces % (numWords-1);
            StringBuffer sb = new StringBuffer();
            sb.append(join(words, left , left + extraSpaces + 1, blank(avgSpaces+1)));
            sb.append(blank(avgSpaces));
            sb.append(join(words, left + extraSpaces + 1,right,  blank(avgSpaces)));
            ans.add(sb.toString());

        }
    }
    
    public String blank(int n){
        StringBuffer sb = new StringBuffer();
        for(int i = 0; i < n; i++){
            sb.append(' ');
        }
        return sb.toString();
    }

    public StringBuffer join(String[] words, int left, int right, String spaces){
        StringBuffer sb = new StringBuffer(words[left]);
        for(int i = left + 1; i < right; i++){
            sb.append(spaces);
            sb.append(words[i]);
        }
        return sb;
    }
}

          sb.append(join(words, left , left + extraSpaces + 1, blank(avgSpaces+1)));
            sb.append(blank(avgSpaces));
            sb.append(join(words, left + extraSpaces + 1,right,  blank(avgSpaces)));

表示的是前extraSpaces个字符串之间的空格大于平均空格1个
打个比方，分苹果，每个字符串代表人，随后的空格个数代表苹果个数，按顺序分，平均分后，剩下的也只有前面的extraSpaces个可以多分
StringBuffer join(String[] words, int left, int right, String spaces) 函数内第一行” StringBuffer sb = new StringBuffer(words[left]);“
其实就是相对于搞了个字符串缓冲区，你加入的字符串和空格，它会逐个给你拼接起来，效果同字符串直接str1+str2，只是用StringBuffer的方式比较好，不用每次拼接的时候底层程序都去创建一个新的字符串。多个空格形成的字符串也可以以stringbuffer.append的方法与之前字符串相接.

join方法本身是将多个变量字符串拼接成一个，跟代码中的空格没关系，结果也不会有空格