CareerCup

Following solution uses a stack ( i.e, some extra space ) .
1. traverse the string , when ever a space is found we can assume we have reached the end of a word . Now , treat this word as a separate string and push it in a stack . Keep on doing so until the string is finished

2. Now pop the stack & put it back into the original string from the start . While doing so , remember to put a space after every single pop , except the last one .

string = "reverse string by words"
    words = string.split()
    words.reverse()
    print " ".join(words)

import java.io.*;
import java.util.*;
public class str1
{
public static void main(String a[])
{
String str="my name is sonam";
String[] s=new String[100];
int i;
StringTokenizer st=new StringTokenizer(str);
int n=st.countTokens();
//st.nextToken();
for(i=0;i<n;i++)
s[i]=st.nextToken();

for(i=n-1;i>=0;i--)
System.out.print(" "+s[i]);
}
}

public static void main(String[] args) {
String str="this is yatra";
String rev = null;
for(int i=(str.length()-1);i>=0;i--){
char ch=str.charAt(i);
rev=String.valueOf(ch);
System.out.print(rev);
}

o/p:artay si siht