//Possible substrings in String.
for(int i=0;i<=input.length();i++){
            for(int j=i+1;j<=input.length();j++){
                System.out.println(input.substring(i,j));
            }
        }

/*Sample Input 1:
Welcome to Coding Ninjas
Sample Output 1:
Ninjas Coding to Welcome
*/
String[] words=input.trim().split("\\\\s+");//Trim removes space, split is before that and after that.
Collections.reverse(Arrays.asList(words));
return String.join(" ",words);