메인 내용으로 이동 # P vs NP

If P=NP, then the world would be a profoundly different place than we usually assume it to be. There would be no special value in "creative leaps," no fundamental gap between solving a problem and recognizing a solution once it's found. Everyone who could appreciate a symphony would be Mozart; everyone who could follow a step-by-step argument would be Gauss. — Scott Aaronson

Simplicity is the final achievement. After one has played a vast quantity of notes and more notes, it is simplicity that emerges as the crowning reward of art. — Chopin

One day, I will find the right words, and they will be simple. — Jack Kerouac

### Hard to Compute, Simple to Verify​

• But relaxing the definition of "hard to compute, simple to verify" lets us make some interesting analogies across different emerging technologies.
• There's public-key cryptography, which relies on things hard to compute, easy-to-verify problems like factorization of large integers, or elliptic curve cryptography
• There are also zero-knowledge proofs, which let counterparties prove that they know ng without revealing the actual secret
• Before LLMs, generating the associated image took time if you were given a prompt. A talented artist could take a few hours (minutes, days, etc.) to create a polished piece. Once created, it would be easy to verify if it fits the criteria - is this an image of a horse wearing sunglasses?
• There are no problems that are easy to compute yet hard to verify. If such a problem existed, you could just re-run the computation again.

One such thing of easy to compute yet hard to verify can be tracking the time-based hash seed, but this is only true depending on the definition of confirming. If verifying means giving input and comparing the output, yes, it is easy. It will be hard if verifying includes finding the information and comparing the production. But then again, it also falls into another hard-to-compute problem.

## P: Poly-time Solvable​

• Class of solvable and verifiable problems in polynomial time by a deterministic Turing machine.

## NP: Nondeterministic Polynomial Time​

• Class of problems that are not sure if it's solvable in polynomial time but verifiable in polynomial time.

• To prove that a problem is in NP, we need an efficient certification: a certificate (a potential solution to the problem) and a certifier (a way to verify the answer in polynomial time).

## NP-Hard: Nondeterministic Polynomial Time-Hard​

• It means "at least as hard as the hardest problems in NP."

• Not sure if it's solvable in poly-time.

• Not sure if it's verifiable in poly-time.

• To prove that a problem is NP-hard, we need to show that it is poly-time reducible to another NP-hard problem. That is, reduce another NP-hard problem in it.

## NP-Complete​

Both NP and NP-Hard.