68. Text Justification

Text Justification

Problem Description

Given an array of strings 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 does 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 because 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                  "
]

 

Constraints:

• 1 <= words.length <= 300
• 1 <= words[i].length <= 20
• words[i] consists of only English letters and symbols.
• 1 <= maxWidth <= 100
• words[i].length <= maxWidth

Approach) 

var fullJustify = function(words, maxWidth) {
    const res = [];
    let lineWords = [];
    let width = maxWidth;
    
    for (let word of words) {
        if (width - lineWords.length >= word.length) {
            lineWords.push(word);
            width -= word.length;
        } else {
            addLineToResults(res, lineWords, width);
            lineWords = [word];
            width = maxWidth - word.length;
        }
    }
    
    if (lineWords.length) {
        let lastLine = lineWords.join(' ');
        lastLine += ' '.repeat(maxWidth - lastLine.length);
        res.push(lastLine);
    }
    
    return res;
};

const addLineToResults = (res, lineWords, width) => {
    if (lineWords.length === 1) {
        const line = lineWords[0] + ' '.repeat(width);
        res.push(line);
        return;
    }
    
    const end = lineWords.length - 1;
    let index = 0;
    while (width > 0) {
        lineWords[index] += ' ';
        index = (index + 1) % end;
        width--;
    }
    
    res.push(lineWords.join(''));
}

Approach) Two Pass

The two-pass version where we preprocess the words into rows is easier to understand:

var fullJustify = function(words, maxWidth) {
    const res = [[]];
    res[0].letters = 0;
    for (let word of words) {
        let row = res[res.length - 1];
        if (row.length && row.letters + row.length + word.length > maxWidth) {
            res.push([]);
            row = res[res.length - 1];
            row.letters = 0;
        }
        row.push(word);
        row.letters += word.length;
    }
    for (let r = 0; r < res.length; r++) {
        let row = res[r];
        if (row.length === 1 || r === res.length - 1) {
            res[r] = row.join(' ') + ' '.repeat(maxWidth - row.letters - row.length + 1);
            continue;
        }
        let line = row[0];
        let spaces = maxWidth - row.letters;
        let minSpaces = ' '.repeat(Math.floor(spaces / (row.length - 1)));
        let addSpace = spaces % (row.length - 1);
        for (let w = 1; w < row.length; w++) {
            line += minSpaces + (w <= addSpace ? ' ' : '') + row[w];
        }
        res[r] = line;
    }
    return res;
};

We can also do this in one pass:

var fullJustify = function(words, maxWidth) {
    for (let res = [[]], i = 0, letters = 0; i <= words.length; letters += words[i++].length) {
        let row = res[res.length - 1];
        if (i === words.length || row.length && letters + row.length + words[i].length > maxWidth) {
            if (row.length === 1 || i === words.length) {
                res[res.length - 1] = row.join(' ') + ' '.repeat(maxWidth - letters - row.length + 1);
                if (i === words.length) return res;
            } else {
                let line = row[0];
                let spaces = maxWidth - letters;
                let minSpaces = ' '.repeat(Math.floor(spaces / (row.length - 1)));
                let addSpace = spaces % (row.length - 1);
                for (let w = 1; w < row.length; w++) {
                    line += minSpaces + (w <= addSpace ? ' ' : '') + row[w];
                }
                res[res.length - 1] = line;
            }
            res.push([]);
            letters = 0;
        }
        res[res.length - 1].push(words[i]);
    }
};

I prefer the longer version, as there isn't any speed/space advantage either way.

Conclusion

That’s all folks! In this post, we solved LeetCode problem 68. Text Justification

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