68.Text-Justification

68. Text Justification

题目地址

https://leetcode.com/problems/text-justification/

题目描述

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

代码

Approach #1

public class Solution {
    public List<String> fullJustify(String[] words, int L) {
        List<String> lines = new ArrayList<String>();

        int index = 0;
        while (index < words.length) {
            int len = words[index].length();
              // 1. 计算每行最大的单词个数
            int lastIdx = index + 1;
            while (lastIdx < words.length) {
                if (words[lastIdx].length() + len + 1 > L) break;
                len += words[lastIdx].length() + 1;
                lastIdx++;
            }

            StringBuilder builder = new StringBuilder();
            int diff = lastIdx - index - 1;
          // 2. 最后一行或者单行只有一个单词，都按作左对齐处理
            // if last line or number of words in the line is 1, left-justified
            if (lastIdx == words.length || diff == 0) {
                for (int i = index; i < lastIdx; i++) {
                    builder.append(words[i] + " ");
                }
                builder.deleteCharAt(builder.length() - 1);
                for (int i = builder.length(); i < L; i++) {
                    builder.append(" ");
                }
            } 
          // 3. 否则根据剩余空间，来计算每个单词间距
          else {
                // middle justified
                int spaces = (L - len) / diff;
               // remaining number of space which we should insert from left to right
                int r = (L - len) % diff; 
                for (int i = index; i < lastIdx; i++) {
                    builder.append(words[i]);
                    if (i < lastIdx - 1) {
                          int total_space = (spaces + ((i - index) < r ? 1 : 0);
                        for (int j = 0; j <= total_space); j++) {
                            builder.append(" ");
                        }
                    }
                }
            }
            lines.add(builder.toString());
            index = lastIdx;
        }

        return lines;
    }
}

Approach #2:

class Solution {
public List<String> fullJustify(String[] words, int maxWidth) {
        int left = 0; List<String> result = new ArrayList<>();

        while (left < words.length) {
            int right = findRight(left, words, maxWidth);
            result.add(justify(left, right, words, maxWidth));
            left = right + 1;
        }

        return result;
    }

    private int findRight(int left, String[] words, int maxWidth) {
        int right = left;
        int sum = words[right++].length();

        while (right < words.length && (sum + 1 + words[right].length()) <= maxWidth)
            sum += 1 + words[right++].length();

        return right - 1;
    }

    private String justify(int left, int right, String[] words, int maxWidth) {
        if (right - left == 0) return padResult(words[left], maxWidth);

        boolean isLastLine = right == words.length - 1;
        int numSpaces = right - left;
        int totalSpace = maxWidth - wordsLength(left, right, words);

        String space = isLastLine ? " " : blank(totalSpace / numSpaces);
        int remainder = isLastLine ? 0 : totalSpace % numSpaces;

        StringBuilder result = new StringBuilder();
        for (int i = left; i <= right; i++)
            result.append(words[i])
                .append(space)
                .append(remainder-- > 0 ? " " : "");

        return padResult(result.toString().trim(), maxWidth);
    }

    private int wordsLength(int left, int right, String[] words) {
        int wordsLength = 0;
        for (int i = left; i <= right; i++) wordsLength += words[i].length();
        return wordsLength;
    }

    private String padResult(String result, int maxWidth) {
        return result + blank(maxWidth - result.length());
    }

    private String blank(int length) {
        return new String(new char[length]).replace('\0', ' ');
    }
}