Top MCQs on NP Complete Complexity with Answers

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Question 1

Let S be an NP-complete problem and Q and R be two other problems not known to be in NP. Q is polynomial time reducible to S and S is polynomial-time reducible to R. Which one of the following statements is true? (GATE CS 2006)
  • R is NP-complete
  • R is NP-hard
  • Q is NP-complete
  • Q is NP-hard
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Question 2

Let X be a problem that belongs to the class NP. Then which one of the following is TRUE?
  • There is no polynomial time algorithm for X.
  • If X can be solved deterministically in polynomial time, then P = NP.
  • If X is NP-hard, then it is NP-complete.
  • X may be undecidable.
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Question 3

The problem 3-SAT and 2-SAT are

  • both in P

  • both NP complete

  • NP-complete and in P respectively

  • undecidable and NP-complete respectively

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Question 4

Which of the following statements are TRUE? (1) The problem of determining whether there exists a cycle in an undirected graph is in P. (2) The problem of determining whether there exists a cycle in an undirected graph is in NP. (3) If a problem A is NP-Complete, there exists a non-deterministic polynomial time algorithm to solve A.
  • 1, 2 and 3
  • 1 and 3
  • 2 and 3
  • 1 and 2
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Question 5

Which of the following statements are TRUE? 

1. The problem of determining whether there exists
   a cycle in an undirected graph is in P.
2. The problem of determining whether there exists
   a cycle in an undirected graph is in NP.
3. If a problem A is NP-Complete, there exists a 
   non-deterministic polynomial time algorithm to solve A.

  • 1, 2 and 3

  • 1 and 2 only

  • 2 and 3 only

  • 1 and 3 only

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Question 6

Suppose a polynomial time algorithm is discovered that correctly computes the largest clique in a given graph. In this scenario, which one of the following represents the correct Venn diagram of the complexity classes P, NP and NP Complete (NPC)?

GATECS2014Q48

  • A

  • B

  • C

  • D

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Question 7

Consider the decision problem 2CNFSAT defined as follows:

GATECS2014Q55

  • NP-Complete.

  • solvable in polynomial time by reduction to directed graph reachability.

  • solvable in constant time since any input instance is satisfiable.

  • NP-hard, but not NP-complete.

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Question 8

Consider the following two problems on undirected graphs 
α : Given G(V, E), does G have an independent set of size | V | - 4?
β : Given G(V, E), does G have an independent set of size 5?
Which one of the following is TRUE?
  • α is in P and β is NP-complete
  • α is NP-complete and β is in P
  • Both α and β are NP-complete
  • Both α and β are in P
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Question 9

Ram and Shyam have been asked to show that a certain problem Π is NP-complete. Ram shows a polynomial time reduction from the 3-SAT problem to Π, and Shyam shows a polynomial time reduction from Π to 3-SAT. Which of the following can be inferred from these reductions ?
  • Π is NP-hard but not NP-complete
  • Π is in NP, but is not NP-complete
  • Π is NP-complete
  • Π is neither NP-hard, nor in NP
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Question 10

Consider two decision problems Q1, Q2 such that Q1 reduces in polynomial time to 3-SAT and 3-SAT reduces in polynomial time to Q2. Then which one of the following is consistent with the above statement?

  • Q1 is in NP, Q2 is NP hard

  • Q2 is in NP, Q1 is NP hard

  • Both Q1 and Q2 are in NP

  • Both Q1 and Q2 are in NP hard

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There are 20 questions to complete.

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