Most of would have heard about this question in interviews and most of our appoches would have been to find the word boundries and copy word by word.
Here is an effecient solution that i came accross.
problem: reverse "the house is blue", the answer should be "blue is house the". the words are reversed, but the letters are still in order (within the word).
solution:
initial: the house is blue
complete string reverse: eulb si esuoh eht
look at the result for a minute. notice anything? if you still don't see it, try this.
initial: the house is blue
reverse: eulb si esuoh eht
wanted : blue is house the
the solution can be attained by first reversing the string normally, and then just reversing each word.