NULL == X is just another coding style used by the programmers to avoid some mistakes in codes.
Whenever people write bigger codes they use to follow these type of convention instead of X == NULL reason being while writing code the programmer may type X = NULL instead of X == NULL which will result in overwriting of X.
While in other case NULL ==X if accidently programmer writes NULL = X then he/she will get a compilation error instead overwriting.
you have to generate features from the tweets.
eg: some hashtag says #serious so you can use this type of info in performing your sentiment analysis.
this question was asked in iit delhi interview,they told to aasume it to be a complete binary tree i answered them 0.5 ^lgn,after this they changed the probablities like 0.75 for right and 0.25 for left
and in the next question they simply said 100% we were going right
they asked is there any case in which one can always land up on the max element in heap,for that i replied yess if all elemnts in last level are same !!