LeetCode（24）文本左右对齐【数组/字符串】【困难】

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1.题目

给定一个单词数组 words 和一个长度 maxWidth ，重新排版单词，使其成为每行恰好有 maxWidth 个字符，且左右两端对齐的文本。

你应该使用 “贪心算法” 来放置给定的单词；也就是说，尽可能多地往每行中放置单词。必要时可用空格 ' ' 填充，使得每行恰好有 maxWidth 个字符。

要求尽可能均匀分配单词间的空格数量。如果某一行单词间的空格不能均匀分配，则左侧放置的空格数要多于右侧的空格数。

文本的最后一行应为左对齐，且单词之间不插入额外的空格。

注意:

单词是指由非空格字符组成的字符序列。
每个单词的长度大于 0，小于等于 maxWidth。
输入单词数组 words 至少包含一个单词。

示例 1:

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

示例 2:

输入:words = ["What","must","be","acknowledgment","shall","be"], maxWidth = 16
输出:
[
  "What   must   be",
  "acknowledgment  ",
  "shall be        "
]
解释: 注意最后一行的格式应为 "shall be    " 而不是 "shall     be",
     因为最后一行应为左对齐，而不是左右两端对齐。       
     第二行同样为左对齐，这是因为这行只包含一个单词。

示例 3:

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

提示:

1 <= words.length <= 300
1 <= words[i].length <= 20
words[i] 由小写英文字母和符号组成
1 <= maxWidth <= 100
words[i].length <= maxWidth

2.答案

class Solution {
    public List<String> fullJustify(String[] words, int maxWidth) {
        if (words.length == 1) {
            int leftSpaceNum = maxWidth - words[0].length();
            char[] leftSpaces = new char[leftSpaceNum];
            Arrays.fill(leftSpaces, ' ');
            return Collections.singletonList(words[0] + new String(leftSpaces));
        }
        List<String> lines = new ArrayList<>();
        int i = 1;
        int length = words[0].length();
        List<String> lineWords = new ArrayList<>();
        lineWords.add(words[0]);
        while (i < words.length) {
            if (length + 1 + words[i].length() <= maxWidth) {
                // 记录每行的单词
                lineWords.add(words[i]);
                length = length + 1 + words[i++].length();
            } else {
                // 已经记满一行
                String line = wordsToLine(lineWords, maxWidth, false);
                lines.add(line);
                lineWords.clear();
                lineWords.add(words[i]);
                length = words[i++].length();
            }
        }
        String line = wordsToLine(lineWords, maxWidth, true);
        lines.add(line);
        return lines;
    }

    /**
        * 将单词转化为一行
        * @param lineWords
        * @return
        */
    private String wordsToLine(List<String> lineWords, int maxWidth, boolean isLastLine) {
        assert lineWords.size() >= 1;
        int wordsLength = lineWords.stream().mapToInt(String::length).sum();
        if (!isLastLine && lineWords.size() > 1) {
            // 非最后一行
            // 计算每个间隔空格
            int eachSpaceNum = (maxWidth - wordsLength) / (lineWords.size() - 1);
            char[] eachSpaces = new char[eachSpaceNum];
            Arrays.fill(eachSpaces, ' ');
            String eachSpaceStr = String.valueOf(eachSpaces);
            // 计算第一个间隔额外空格数
            int leftSpaceNum = (maxWidth - wordsLength) % (lineWords.size() - 1);
            StringBuilder builder = new StringBuilder();
            for (int i = 0; i < lineWords.size(); i++) {
                builder.append(lineWords.get(i));
                if (i != lineWords.size() - 1) {
                    builder.append(eachSpaceStr);
                    if (leftSpaceNum > 0) {
                        builder.append(" ");
                        leftSpaceNum--;
                    }
                }
            }
            return builder.toString();
        } else {
            // 最后一行，左对齐即可
            StringBuilder builder = new StringBuilder();
            for (int i = 0; i < lineWords.size(); i++) {
                builder.append(lineWords.get(i));
                if (i != lineWords.size() - 1) {
                    builder.append(" ");
                }
            }
            int leftSpaceNum = maxWidth - wordsLength - (lineWords.size() - 1);
            char[] leftSpaces = new char[leftSpaceNum];
            Arrays.fill(leftSpaces, ' ');
            builder.append(new String(leftSpaces));
            return builder.toString();
        }
    }
}