Contest Experiences: Codeforces Round #888 (Div. 3)

About Contest:

• The contest was conducted by code forces rated for Div 3 Participants.
• In the contest, there are 7 problems and 2 hours and 15 minutes to solve them.
• The penalty for the wrong submission in this round is 10 minutes.

My contest experiences:

Problem	Difficulty	Topic	Approx time to solve	Number of submissions by me
Escalator Conversations	Easy	Implementation, Hashing	10 – 15 minutes	1
Parity Sort	Easy	Sorting, Two Pointer	8 – 10 minutes	1
Tiles Comeback	Medium	Greedy	20-22 minutes	1
Prefix Permutation Sums	Medium	Math, Implementation	30 – 35 minutes	1

Link of the Contest: Codeforces Round #888 (Div. 3)

Question 1: Escalator Conversations:

• This is an easy question based on implementation and Hashing.
• I thought the only condition to make conversation with a person is the difference between Vlad’s height and the person’s height should be equal to the difference between escalators’ steps’ height.
• So I stored all the differences of steps in a map and then just searched the height difference between Vlad and people if this difference is found then we increment the count.

Question 2: Parity Sort:

• This is an Easy question based on sorting and implementation.
• I made a copy of the original array and then sort the array in non-decreasing order.
• After sorting I checked for the parity of the ith index of both the original and sorted one if the parity is different then I can not apply the operation so the answer is NO.

Question 3: Tiles Comeback:

• This is a medium-level question based on Greedy.
• What comes to my mind after reading the question is I can select any length which should be divisible by K. I tried to take only the minimum possible path length.
  • If the first and last characters are the same then I only need K elements of the same color as the first element.
  • Else, I need a minimum of K elements of the color type of the first element and then after this point, I need a minimum of K elements of the color type of the last element.

Question 4: Prefix Permutation Sums:

• This is a good medium-level question based on the understanding of math and implementation and observation.
• My observation here was that we get array elements by subtracting adjacent elements of its prefix sum array but it is also possible that I can get a difference greater than N which is not the array element this is due to a missing element from the prefix sum array.
• As only one number is missing then we can have only one difference that is greater than N if there is more than one then the answer is NO.
  • Initially, I took a set in which 1 to N elements are inserted so as soon as I get the difference in the set then erase the element.
  • Finally, take the sum of the remaining elements of the set and check it is equal to the one difference which is greater than N if it is equal then the Answer is Yes else NO.