#include "s0151_reverse_words_in_a_string.hpp"

void S0151::reverseSubStr(string &s, int begin, int end) {
  for (; begin < end; ++begin, --end) {
    char tmp = s[begin];
    s[begin] = s[end];
    s[end] = tmp;
  }
}

string S0151::reverseWords(string s) {
  if (s.length() == 0) {
    return s;
  }
  // remove extra spaces
  int len = s.length();
  int slow{0};
  for (int fast{0}; fast < len; ++fast) {
    if (s[fast] != ' ') {
      s[slow++] = s[fast];
    } else {
      if (fast == len - 1) {
        break;
      } else {
        if (s[fast + 1] != ' ' && slow != 0) {
          s[slow++] = ' ';
        }
      }
    }
  }
  s.resize(slow);
  // reverse the whole string
  len = s.length();
  reverseSubStr(s, 0, len - 1);
  // reverse each words
  for (int begin{0}, end{0}; end < len; ++end) {
    if (end == len - 1) {
      reverseSubStr(s, begin, end);
    } else {
      if (s[end + 1] == ' ') {
        reverseSubStr(s, begin, end);
        begin = end + 2;
        end = end + 1;
      }
    }
  }
  return s;
}