my solution to the classic interview question: "reverse the words in a string , and keep the characters' order within a word unchanged."

reverse_words

/*
 * =====================================================================================
 *
 *       Filename:  reverse_words.cpp
 *
 *    Description:  a program to reverse the words in a sentence.
 *
 *        Version:  1.0
 *        Created:  10/27/2013 08:21:49 PM
 *       Revision:  none
 *       Compiler:  gcc
 *
 *         Author:  Ji.Zhilong (), [email protected]
 *   Organization:  SJTU
 *
 * =====================================================================================
 */

#include <iostream>
#include <algorithm>
#include <vector>
#include <cstring>

using std::cin;
using std::cout;
using std::endl;
using std::vector;
using std::swap;

inline void 
reverse_chars(char *arr, int len)
{
  if (arr == NULL || len <= 1)
    return;
  for (int i= 0, j = len - 1; i < j; i++, j--) {
    swap(arr[i], arr[j]);
  }
}

void 
reverse_words(char *arr, int len)
{
  if (arr == NULL || len <= 1)
    return;

  int se[2];  /* storing the start and end indices of words. */
  unsigned short k = 0; /* store indices as word start or word end. */
  bool spacing = true; /* a flag indicates if the last charcter if a space */

  reverse_chars(arr, len);

  for (int i = 0; i < len; i++) {
    if (spacing ^ arr[i] == ' ') {
      spacing = !spacing;
      se[k++] = i;
    }
    if (k == 2) {   /* a whole word encounted, normalize it */
      reverse_chars(&arr[se[0]], se[1] - se[0]);
      k = 0;
    }
  }

  if (!spacing)
    reverse_chars(&arr[se[0]], len - se[0]);
}

int
main(int argc, char *argv[])
{
  int len = strlen(argv[1]);
  reverse_words(argv[1], len);
  cout << argv[1];
}