public class Solution {
public void reverseWords(char[] array, int startIndex, int endIndex) {
		while (startIndex < endIndex) {
			char p = array[startIndex];
			array[startIndex] = array[endIndex];
			array[endIndex] = p;
			startIndex++;
			endIndex--;
		}
	}
	public String reverseWords(String s) {
		if(s==null)
			return null;
		s=s.trim();
		if(s.length()==0)
			return s;
		StringBuilder pString=new StringBuilder(s.length());
		pString.append(s.charAt(0));
		for(int i=1;i<s.length();i++){
			pString.append(s.charAt(i));
			if(s.charAt(i)==' '){
				while(s.charAt(i)==' ')
					i++;
				i--;
			}
		}
		char[] array = pString.toString().toCharArray();
		reverseWords(array, 0, array.length - 1);
		int startIndex = 0;
		int endIndex;
		while (startIndex<array.length) {
			for (endIndex = startIndex + 1; endIndex < array.length; endIndex++) {
				if (array[endIndex] == ' ')
					break;
			}
			reverseWords(array,startIndex,endIndex-1);
			startIndex=endIndex+1;
		}
		return new String(array);
	}
}