Give this problem a try 68. Text Justification.

Problem Statement

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

Prerequisite Knowledge

• Implementation
• String Manipulation

Example Code

class Solution {
    public List<String> fullJustify(String[] words, int maxWidth) {
        int n = words.length;
        List<String> answer = new ArrayList<>();
        StringBuilder sb = new StringBuilder();

        int curWidth = 0;
        int wordCount = 0;
        for (int i = 0; i < n; i++) {
            int candWidth = words[i].length();
            if (curWidth + candWidth + wordCount <= maxWidth) {
                curWidth += candWidth;
                wordCount++;
            }
            else {
                int extraSpaces = maxWidth - curWidth;
                if (wordCount == 1) {
                    sb = new StringBuilder();
                    sb.append(words[i-1]);
                    for (int j = 0; j < extraSpaces; j++) sb.append(" ");
                    answer.add(sb.toString());
                }
                else {
                    sb = new StringBuilder();
                    // distribute extraSpaces to wordCount - 1
                    int[] alloc = new int[wordCount-1];
                    extraSpaces -= (wordCount - 1);
                    for (int j = 0; j < wordCount - 1; j++) alloc[j] = 1;
                    
                    // allocate remaining extraSpaces
                    while (extraSpaces > 0) {
                        for (int j = 0; j < wordCount - 1; j++) {
                            alloc[j]++;
                            extraSpaces--;
                            if (extraSpaces == 0) break;
                        }
                    }

                    for (int j = i - wordCount; j < i - 1; j++) {
                        sb.append(words[j]);
                        for (int k = 0; k < alloc[j - (i - wordCount)]; k++) sb.append(" ");
                    }
                    sb.append(words[i-1]);
                    answer.add(sb.toString());
                }
                curWidth = candWidth;
                wordCount = 1;
            }
        } 

        int extraSpaces = maxWidth - curWidth - (wordCount - 1);
        sb = new StringBuilder();
        for (int i = n - wordCount; i < n-1; i++) sb.append(words[i]).append(" ");
        sb.append(words[n-1]);
        for (int i = 0; i < extraSpaces; i++) sb.append(" ");
        answer.add(sb.toString());

        return answer;
    }
}

Complexity Analysis

• Time Complexity: within O(1e7)
• Space Complexity: O(n)

Sign-off

Congratulations on making it this far! In my view, this problem is rated hard mainly because the implementation can be quite tricky, rather than due to any exceptional algorithmic insight. Best of luck in your future competitions!