whenever you are doing a question in which addition to a string requires , that is , we have to add an character into a string or we have to insert into a stack. Then instead of using '+' operator go for push_back. this help in lot of questions where you are doing a lot of '+' operation in a string. i got this when i was solving a question on geeks and i found TLE many times. Then I tried roughly push_back, and BOOM it worked XD. Thats where i learnt when you are not getting your answer when you are right , then go for rough guesses.

HAPPY CODING :)