Contest Experience: Codeforces Round 891 (Div. 3)

About The Contest:

This Contest was organized on 7 August 2023 on Codeforces. The Contest consisted of 7 problems and had a duration of 2 hours and 15 minutes. The contest had around 40k registrations which was the most for any Div 3 contest till now on Codeforces.

Contest Link: Codeforces Round 891 (Div. 3)

My Experience:

I was able to solve 6 out of 7 problems during the contest.

Problem Name	Topic	Difficulty	Time Taken	No. of Submissions
Array Coloring	Greedy, Maths	Easy	5 mins	1
Maximum Rounding	Greedy, Implementation, Maths	Medium	30 mins	1
Assembly via Minimums	Greedy, Sorting	Easy	15 mins	1
Strong Vertices	Sorting, Maths	Easy-Medium	10 mins	2
Power of Points	Sorting, Maths	Medium	45 mins	1
Sum and Product	Hashing, Maths	Medium	25 mins	1

Problem A: Array Coloring

This was the easiest question of the contest. We just had to check whether the total sum of the array is even or odd. If the total sum comes out to be even then it is always to color the elements of the array using two colors such that their parity is the same and the answer will be Yes otherwise No.

Problem B: Maximum Rounding

Surprisingly, I found this question really complicated. The problem statement was really confusing and it took me a lot of time to really figure out what actually had to be done. Once I finally understood, I just iterated from behind, and if a character greater than 5 was found the previous character was incremented by 1. If the previous character was 9 in that case we have to search for the character less than 9. The implementation was also not really straightforward and the problem was above the level of a normal Div-3 B problem and took me more than 30 minutes to solve it.

Problem C: Assembly via Minimums

This Problem was much simpler than Problem B. I just stored all the elements along their frequencies in an array of pairs and sorted that array in ascending order according to values. Then I just iterated the array and from the frequency of each element, it was determined how many times that element will be present in the final answer. It took me around 5 minutes to implement the above idea.

Problem D: Strong Vertices

This was again a really straightforward problem for me as I had solved this type of problem in the past. By looking into the problem I just transformed the equation A_u-A_v>=B_u-B_v to A_u-B_u>=A_v-B_v. Now I stored A_i-B_i for each i from 1 to N and sorted the array in decreasing order along with indexes and the final answer was the elements that were equal to the largest element.

I made one wrong submission because I did not print the vertices in increasing order as was mentioned in the problem. But still, it took me less time to solve this problem comparedhad to Problem B and Problem C.

Problem E: Power of Points

This was the most interesting problem for me in the contest. After reading the problem statement for the first time,II got the idea that the problem would be solved by maintaining a prefix and suffix array. But still, it took me around 30 minutes to think of the correct approach and how to implement it. The implementation part didn’t take much time as it was required to sort the coordinates and maintain the prefix and suffix sum. It took me around 40 minutes to solve this problem.

Problem F: Sum and Product

By the time I reached Problem F, only 20 minutes were remaining in the contest and it was really challenging for me to solve the problem in that space of time. The problem was a standard mathematical problem as in each query a+b=x and a*b=y were given. I solved this using a quadratic equation and to find the total possible solutions, I used an unordered map in C++ to store the frequency of each element in the array.

Conclusion

Due to 7 problems, it took me more than 2 hours to finish it. I got accepted just 5 minutes before the end of the contest.