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Let S be an NP-complete problem. Q and R are other two problems not known to be NP. Q is polynomial time reducible to S and S is polynomial time reducible to R. Which of the following statements is true?
  • a)
    R is NP-complete
  • b)
    R is NP-hard
  • c)
    Q is NP-complete
  • d)
    Q is NP-hard
Correct answer is option 'B'. Can you explain this answer?
Most Upvoted Answer
Let S be an NP-complete problem. Q and R are other two problems not kn...
Overview:
In this scenario, we are given that problem S is NP-complete, and problems Q and R are not known to be NP. It is also known that Q is polynomial time reducible to S, and S is polynomial time reducible to R. We need to determine which of the following statements is true.

Explanation:
To understand the answer, let's break down the given information and the options provided:

1. S is NP-complete:
This means that S is one of the hardest problems in the class of NP problems. Any problem in NP can be reduced to S in polynomial time.

2. Q is polynomial time reducible to S:
This means that there exists a polynomial time reduction from problem Q to problem S. In other words, we can transform instances of Q into instances of S in polynomial time.

3. S is polynomial time reducible to R:
This means that there exists a polynomial time reduction from problem S to problem R. In other words, we can transform instances of S into instances of R in polynomial time.

Now, let's analyze the given options:

a) R is NP-complete:
We cannot conclude that R is NP-complete because it is not known whether R is in NP or not. The reduction from S to R only tells us that R is at least as hard as S.

b) R is NP-hard:
This statement is true. Since S is NP-complete and there exists a polynomial time reduction from S to R, we can conclude that R is NP-hard. NP-hardness means that a problem is at least as hard as the hardest problems in NP, even if it is not in NP itself.

c) Q is NP-complete:
We cannot conclude that Q is NP-complete because it is not known whether Q is in NP or not. The reduction from Q to S only tells us that S is at least as hard as Q.

d) Q is NP-hard:
We cannot conclude that Q is NP-hard because it is not known whether Q is in NP or not. The reduction from Q to S only tells us that S is at least as hard as Q.

Conclusion:
Based on the given information and the definitions of NP-complete and NP-hard, the correct statement is option 'B' - R is NP-hard.
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Community Answer
Let S be an NP-complete problem. Q and R are other two problems not kn...
  • If the NP-Hard problem is reducible to another problem in polynomial time, then that problem is also NP-hard which means every NP problem can be reduced to this problem in polynomial time.
  • If Q is reducible to S in polynomial time, Q could be NP because all NP problems can be reduced to S. Since Q could be Np therefore Q could be P also as P is a subset of NP. Also, Q could be NPC because every NPC problem can be reduced to another NPC problem in polynomial time. 
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Understanding the Complexity ClassesIn computational theory, problems are categorized into complexity classes based on the resources required to solve them. Here, we focus on four specific problems: PATH, HAMPATH, SAT, and 3SAT, to determine which belong to class P.What is Class P?- Class P consists of decision problems that can be solved by a deterministic Turing machine in polynomial time.- If a problem is in P, it means there exists an algorithm that can solve it efficiently for all input sizes.Analysis of Each Problem- PATH: - The problem asks whether there exists a path between two vertices in a graph. - This can be solved using Depth-First Search (DFS) or Breadth-First Search (BFS), both of which run in polynomial time. - Conclusion: PATH is in P.- HAMPATH: - This problem involves determining whether there is a Hamiltonian path in a graph (a path that visits each vertex exactly onc e). - HAMPATH is NP-complete, meaning it is not known to be solvable in polynomial time. - Conclusion: HAMPATH is not in P.- SAT (Satisfiability): - SAT asks whether a boolean formula can be satisfied by some assignment of truth values. - While SAT is NP-complete, it was proven to be in NP, and due to advancements, it can be solved in polynomial time for specific cases. - Conclusion: SAT is not in P generally.- 3SAT: - This is a specific case of SAT where the formula is in conjunctive normal form with exactly three literals per clause. - 3SAT is also NP-complete and does not have known polynomial-time solutions. - Conclusion: 3SAT is not in P.Final ConclusionBased on the analyses, the problems that belong to class P are:- Option A: SAT - Not generally in P.- Option C: PATH - In P.Thus, only PATH is confirmed to be in P.

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Let S be an NP-complete problem. Q and R are other two problems not known to be NP. Q is polynomial time reducible to S and S is polynomial time reducible to R. Which of the following statements is true?a)R is NP-completeb)R is NP-hardc)Q is NP-completed)Q is NP-hardCorrect answer is option 'B'. Can you explain this answer?
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