2 Test Cases failed

#1

Hi,

My approach is like, I am checking whether the sequence is either totally increasing or totally decreasing but it fails to pass all the test cases.

  1. If my approach is correct so what condition i have to add?

  2. If my approach is incorrect so How should i approach this question ?, As in question it mentioned not to use array and list, so the best possible i think is this.

Thank You.

#2

When the sequence is first strictly decreasing then strictly increasing.
For example :
9 5 2 7 10
The sequence first decreases starting from 9 to 2 - { 9, 5, 2 } and then starts increasing - { 7, 10}. Note that it can also be broken as { 9, 5} and { 2, 7, 10} .
Since the sequence fulfills the required condition , we would also print “true” for this.

#3

@aa1 Thanks for elaborating the question Ma’am but still i didn’t get, how can i separate the sequences without the use of array and list , so as to check whether the sequence is decreasing increasing. Could you please tell me, How to approach this ?

#4

About the input, you need not to take array, one can also perform the question without using array. As every time we just check two consecutive numbers to tell whether the seqeunce is increasing or decreasing, so why should we store all of the numbers.

  • A sequence is true if you can split it into two sub sequence such that first sequence is strictly increasing and second sequence is strictly decreasing.
  • For e.g.,
    1 2 3 4 5
    This sequence is also true as we can split it into two sequence like., sequence one is empty and sequence two is 1 2 3 4 5.
  • Let’s take another example.,
    5 4 3 2 1
    This is also true as we can split it such that sequence one is5 4 3 2 1 and sequence two is empty.
    According to the problem statement, we can say the if the sequence decreases then it should not increase, if this is the case one can directly print false else print true.
  • The third case is when the sequence is first strictly decreasing then strictly increasing.
    For example :
    9 5 2 7 10
    The sequence first decreases starting from 9 to 2 - { 9, 5, 2 } and then starts increasing - { 7, 10}. Note that it can also be broken as { 9, 5} and { 2, 7, 10} .
    Since the sequence fulfills the required condition , we would also print “true” for this.

If a sequence does not meet any of the above criteria , we return “false” for it.

Implementation : First we assume that our sequence is decreasing only. We also assume that our sequence is initially valid and only try to disprove it during the course.
We compare our current element with the previous element and based on that comparison make our decision.
If the curr element is equal to the prev element , we see that the sequence is neither strictly increasing or decreasing so we mark our sequence as invalid.
If the curr element is greater than the prev element, then we realise that the sequence has started increasing and we mark it so using a flag variable “goingUp” which we had initially marked as false based on our assumption that the sequence is decreasing.
If the curr element is less than the previous element and the current sequence is also proceeding as decreasing , we are to do nothing. However if the current sequence is increasing and we get a pair for a decreasing sequence then we mark our sequence as invalid since we cannot have a decreasing part after the increasing sequence.
After each iteration , store the value of the curr element into the prev element so that we can compare it with the next input element.

1 Like
#5

@aa1, I made changes in my code according to the above explanation

My code is working fine for these testcases

i) 1 2 3 4 5 — > returns True

ii) 5 4 3 2 1 ----- > returns True

iii) 9 5 2 7 10 — > returns True // decreasing then increasing (Allowed A. T. Q)

iv) 1 2 3 2 1 — > returns false // As decreasing after increasing not allowed

v) 1 ---- > returns true

but still 2 test cases are saying “wrong answer”

#6

@aa1 could you please comment out in my code, where i am going wrong ?