The concept of polynomial-time reduction is central to understanding the structure of NP-complete problems.
Fearless is not the absence of fear. It’s not being completely unafraid. To me, fearless is having fears. Fearless is having doubts. Lots of them. To me, fearless is living in spite of those things that scare you to death.
不追忆过去,不忧虑未来,也不贪恋现在。