reverseWordsInAString.II.cpp

// Source : https://oj.leetcode.com/problems/reverse-words-in-a-string-ii/
// Author : Hao Chen
// Date   : 2015-02-09

/********************************************************************************** 
 * 
 * Given an input string, reverse the string word by word. A word is defined as a sequence of non-space characters. 
 * 
 * The input string does not contain leading or trailing spaces and the words are always separated by a single space. 
 * 
 * For example,
 *  Given s = "the sky is blue",
 *  return "blue is sky the". 
 * 
 * Could you do it in-place without allocating extra space? 
 * 
 * 
 **********************************************************************************/

#include <ctype.h>
#include <iostream>
#include <string>
using namespace std;


void swap(char &a, char &b) {
    char temp = a;
    a = b;
    b = temp;
}
void reverse(string &s, int begin, int end) {
    while(begin < end) {
        swap(s[begin++], s[end--]);
    }
}
void reverseWords(string &s) {

    if (s.size()<=1) return;

    // reverse the whole string
    reverse(s, 0, s.size()-1);

    // reverse the each word
    for ( int begin=0, i=0; i<=s.size(); i++ ) {
        if ( isblank(s[i]) || s[i] == '\0') {
            reverse(s, begin, i-1);
            begin = i+1;
        }
    }
}


int main(int argc, char** argv)
{
    string s = "the sky is blue";
    if ( argc > 1 ) {
        s = argv[1];
    }
    
    cout << s << endl;
    reverseWords(s);
    cout << s << endl;
    
}