Justify the given Text based on the given width of each line

Given a string str and width of each line as L, the task is to justify the string such that each line of justified text is of length L with help of space (‘ ‘) and the last line should be left-justified.

Examples:

Input: str = “GeeksforGeek is the best computer science portal for geeks.”, L = 16
Output:
GeeksforGeek__is
the_________best
computer_science
portal_______for
geeks.__________

Input: str = “The quick brown fox jumps over the lazy dog.”, L = 11
Output:
The___quick
brown___fox
jumped_over
the____lazy
dogs.______
The symbol _ denotes a space.

Approach:
The number of spaces between words in each line cannot be computed until a complete set of words in that line is known. We will solve this problem on a line-by-line basis.



  1. Split the given text into words
  2. Firstly select the words which can be inserted in each line including a space between each word. For that, the sum of length of included words with one space between them must be smaller than or equal to L.
  3. Now count the number of spaces needed to make the length of each line L and distribute the spaces evenly.
  4. Repeat above steps for next set of words.
  5. For the last line spaces must be assigned at the end as the last line must be left-justified.

Below is the implementation of the above approach:

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// C++ program to Justify the given Text
// according to the given width of each line
  
#include "bits/stdc++.h"
using namespace std;
  
// Function to join the words
// with spaces spread evenly
string JoinALineWithSpace(
    vector<string>& words,
    int start, int end,
    int num_spaces)
{
  
    // Number of words in current line
    int num_words_curr_line
        = end - start + 1;
  
    // String to store the justified text
    string line;
  
    for (int i = start; i < end; i++) {
  
        line += words[i];
        --num_words_curr_line;
  
        // Count number of current space needed
        int num_curr_space
            = ceil((double)(num_spaces)
                   / num_words_curr_line);
  
        // Insert spaces in string line
        line.append(num_curr_space, ' ');
  
        // Delete the spaces inserted in line
        num_spaces -= num_curr_space;
    }
  
    // Insert word to string line
    line += words[end];
    line.append(num_spaces, ' ');
  
    // Return justified text
    return line;
}
  
// Function that justify the words of
// sentence of length of line L
vector<string> JustifyText(
    vector<string>& words,
    int L)
{
  
    int curr_line_start = 0;
    int num_words_curr_line = 0;
    int curr_line_length = 0;
  
    // To store the justified text
    vector<string> result;
  
    // Traversing the words array
    for (int i = 0; i < words.size(); i++) {
  
        // curr_line_start is the first word
        // in the current line, and i is
        // used to identify the last word
        ++num_words_curr_line;
  
        int lookahead_line_length
            = curr_line_length
              + words[i].size()
              + (num_words_curr_line - 1);
  
        // If by including the words length becomes L,
        // then that set of words is justified
        // and add the justified text to result
        if (lookahead_line_length == L) {
  
            // Justify the set of words
            string ans
                = JoinALineWithSpace(
                    words,
                    curr_line_start,
                    i,
                    i - curr_line_start);
  
            // Store the justified text in result
            result.emplace_back(ans);
  
            // Start the current line
            // with next index
            curr_line_start = i + 1;
  
            // num of words in the current line
            // and current line length set to 0
            num_words_curr_line = 0;
            curr_line_length = 0;
        }
  
        // If by including the words such that
        // length of words becomes greater than L,
        // then hat set is justified with
        // one less word and add the
        // justified text to result
        else if (lookahead_line_length > L) {
  
            // Justify the set of words
            string ans
                = JoinALineWithSpace(
                    words,
                    curr_line_start,
                    i - 1,
                    L - curr_line_length);
  
            // Store the justified text in result
            result.emplace_back(ans);
  
            // Current line set to current word
            curr_line_start = i;
  
            // Number of words set to 1
            num_words_curr_line = 1;
  
            // Current line length set
            // to current word length
            curr_line_length = words[i].size();
        }
  
        // If length is less than L then,
        // add the word to current line length
        else {
            curr_line_length
                += words[i].size();
        }
    }
  
    // Last line is to be left-aligned
    if (num_words_curr_line > 0) {
        string line
            = JoinALineWithSpace(
                words,
                curr_line_start,
                words.size() - 1,
                num_words_curr_line - 1);
  
        line.append(
            L - curr_line_length
                - (num_words_curr_line - 1),
            ' ');
  
        // Insert the last line
        // left-aligned to result
        result.emplace_back(line);
    }
  
    // Return result
    return result;
}
  
// Function to insert words
// of sentence
vector<string> splitWords(string str)
{
  
    vector<string> words;
    string a = "";
    for (int i = 0; str[i]; i++) {
  
        // Add char to string a
        // to get the word
        if (str[i] != ' ') {
            a += str[i];
        }
  
        // If a space occurs
        // split the words and
        // add it to vector
        else {
            words.push_back(a);
            a = "";
        }
    }
  
    // Push_back the last word
    // of sentence
    words.push_back(a);
  
    // Return the vector of
    // words extracted from
    // string
    return words;
}
  
// Function to print justified text
void printJustifiedText(vector<string>& result)
{
    for (auto& it : result) {
        cout << it << endl;
    }
}
  
// Function to call the justification
void justifyTheText(string str, int L)
{
  
    vector<string> words;
  
    // Inserting words from
    // given string
    words = splitWords(str);
  
    // Function call to
    // justify the text
    vector<string> result
        = JustifyText(words, L);
  
    // Print the justified
    // text
    printJustifiedText(result);
}
  
// Driver Code
int main()
{
    string str
        = "GeeksforGeek is the best"
          " computer science portal"
          " for geeks.";
    int L = 16;
  
    justifyTheText(str, L);
  
    return 0;
}

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Output:

GeeksforGeek  is
the         best
computer science
portal       for
geeks.

Time Complexity: O(N), where N = length of string

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