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95. Text Justification

hardAsked at Salesforce

Format text such that each line has exactly maxWidth characters with full justification. Salesforce uses this as a string-manipulation stress test.

By Alex Chen, Founder, InterviewChamp.AI · Last verified

Source citations

Public interview reports confirming this problem appears in Salesforce loops.

  • Glassdoor (2026-Q1)— Salesforce uses text formatting in their email template rendering.
  • Blind (2025)— Hard string-manipulation onsite question.

Problem

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. The last line of text should be left-justified, and no extra space is inserted between words.

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

Examples

Example 1

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

Approaches

1. Two-pass: select then format

First pass: group words into lines. Second pass: format each line.

Time
O(n)
Space
O(n)
function fullJustify(words, maxWidth) {
  const result = [];
  let i = 0;
  while (i < words.length) {
    let lineLen = words[i].length, j = i + 1;
    while (j < words.length && lineLen + 1 + words[j].length <= maxWidth) {
      lineLen += 1 + words[j].length;
      j++;
    }
    const lineWords = words.slice(i, j);
    const gaps = lineWords.length - 1;
    let line;
    if (gaps === 0 || j === words.length) {
      line = lineWords.join(' ') + ' '.repeat(maxWidth - lineLen);
    } else {
      const totalSpaces = maxWidth - lineWords.reduce((s, w) => s + w.length, 0);
      const base = Math.floor(totalSpaces / gaps), extra = totalSpaces % gaps;
      line = lineWords.reduce((acc, w, idx) => {
        if (idx === 0) return w;
        return acc + ' '.repeat(base + (idx <= extra ? 1 : 0)) + w;
      }, '');
    }
    result.push(line);
    i = j;
  }
  return result;
}

Tradeoff: Greedy line-packing + per-line distribution. Salesforce wants both passes done cleanly.

2. Single pass with running buffer

Process word by word; emit when adding next would overflow.

Time
O(n)
Space
O(n)
// Similar shape. Mostly identical to two-pass.

Tradeoff: No advantage over two-pass.

Salesforce-specific tips

Salesforce uses text justification in email-template rendering and dashboard display. They grade on three things: (1) greedy line-packing logic, (2) extra-space distribution among gaps (extra spaces go to leftmost gaps first), (3) last-line special case (left-justified, no inter-word padding). Bonus signal: walk through the case where a line has only one word — must left-justify and pad with trailing spaces.

Common mistakes

  • Forgetting the last-line special case — must be left-justified.
  • Distributing extra spaces randomly instead of leftmost-first.
  • Off-by-one on lineLen accumulation (+1 for the space).

Follow-up questions

An interviewer at Salesforce may pivot to one of these next:

  • Optimal line-breaking with cost function (Knuth's algorithm).
  • Soft-wrap a large block of text into a fixed width.
  • Render markdown into fixed-width text.

Solve it now

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Output

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FAQ

Why are extra spaces distributed leftmost-first?

Convention — leftmost gaps get rounded-up shares. So if there are 7 spaces over 3 gaps, the first gap gets 3, the second and third get 2 each.

What if a single word equals maxWidth?

It fills the line by itself, no spaces needed. Edge case worth confirming with the interviewer.

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