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ISRO-DEC2017-47

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3 votes
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Which of the following permutation can be obtained in the same order using a stack assuming that
input is the sequence $5,6,7,8,9$ in that order?

  1. $7,8,9,5,6$
  2. $5,9,6,7,8$
  3. $7,8,9,6,5$
  4. $9,8,7,5,6$
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1 Answer

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5 votes

Option A can't be true because 6 cannot be popped after 5 when 5 is coming before 6.

Option B can't be true too because 6 can't be popped before 7 or 8.

Option C is possible:
Push 5
Push 6
Push 7        Pop 7
Push 8        Pop 8
Push 9        Pop 9
                    Pop 6
                    Pop 5

Option D can't be true because 5 is getting popped before 6.

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