LeetCode 68. Text Justification

This is actually not the LeetCode version answer. But I think this is more likely in real word.

The Code is copied from the EPI.  I have no clue to solve this problem at the first sight.

#include <string>#include <vector>#include <iostream>#include <cmath>using namespace std;/*  Example:  words = ["This", "is", "an", "example", "of", "text", "justification"]  L : 16  return   [   "This    is    an",   "example  of text",   "justification.  "  ]*/string JoinALineWithSpace(vector<string>& words, int start, int end, int numSpaces) {  size_t num_words_curr_line = end - start + 1;  string line;  for(int i = start; i < end; ++i) {    line += words[i];    --num_words_curr_line;    size_t num_curr_space = ceil(static_cast<double>(numSpaces)/num_words_curr_line);    line.append(num_curr_space, ' ');    numSpaces -= num_curr_space;  }  line += words[end];  line.append(numSpaces, ' ');  return line;}vector<string> fullJustify(vector<string>& words, int maxWidth) {  int maxLen = 0;  for(int i = 0; i < words.size(); ++i) {      if(words[i].size() > maxLen) maxLen = words[i].size();  }  if(maxLen > maxWidth) return {};  vector<string> res;  int num_words_curr_line = 0;  int curr_line_length = 0;  int curr_line_start = 0;  for(int i = 0; i < words.size(); ++i) {    ++num_words_curr_line;    size_t lookahead_line_length = curr_line_length + words[i].size() + (num_words_curr_line - 1);    if(lookahead_line_length == maxWidth) {      res.push_back(JoinALineWithSpace(words, curr_line_start, i, i - curr_line_start));      curr_line_start = i + 1;      curr_line_length = 0;      num_words_curr_line = 0;    } else if(lookahead_line_length > maxWidth) {      res.push_back(JoinALineWithSpace(words, curr_line_start, i - 1, maxWidth - curr_line_start));      curr_line_start = i;      curr_line_length = words[i].size();      num_words_curr_line = 1;    } else {      curr_line_length += words[i].size();    }  }  if(num_words_curr_line > 0) {    string line = JoinALineWithSpace(words, curr_line_start, words.size() - 1, num_words_curr_line - 1);    line.append(maxWidth - curr_line_length - (num_words_curr_line - 1), ' ');    res.push_back(line);  }  return res;}int main(void) {  vector<string> words{"This", "is", "an", "example", "of", "text", "justification"};  vector<string> res = fullJustify(words, 16);  for(int i = 0; i < res.size(); ++i) cout << res[i] << endl;}