I have recently started to attend the online coding contest. Leetcode has held weekly contests on Sunday early mornings - which isn't ideal for coders living in Europe.

However, they have biweekly contests, which is run the Sat 3:30 to 5:30 (BST) every two weeks.

Today's contest: https://leetcode.com/contest/biweekly-contest-31

I have managed to solve 3 puzzles in 30 minutes, however, failed to solve the fourth puzzle (difficulty level) in next hour. 

The programming language I choose is C++. I have 2  Wrong Answer submission for Problem 2 - which adds total 10 minutes time penalization.

![image.png](https://cdn.steemitimages.com/DQmSYHXx4SCNu39BC8HovjteMYc5FF6s3DFys2iL9XcVPHz/image.png)

The fourth puzzle is not that difficult - it is a pity that I didn't get it - and my ranking is expected to drop.

## Count Odd Numbers in an Interval Range
https://leetcode.com/contest/biweekly-contest-31/problems/count-odd-numbers-in-an-interval-range
Easy Math, we can simplify the problem by adjusting the low/high acordingly. For example, when low is even, we can increment the low and the result will be the same.

## Number of Sub-arrays With Odd Sum
https://leetcode.com/contest/biweekly-contest-31/problems/number-of-sub-arrays-with-odd-sum/
Dynamic Programming or Prefix Sum. Count the even sum or odd sum and add them.

## Number of Good Ways to Split a String
https://leetcode.com/contest/biweekly-contest-31/problems/number-of-good-ways-to-split-a-string/
Use two arrays to store the number of occurencies for each character. There are O(N) ways to split a string.

## Minimum Number of Increments on Subarrays to Form a Target Array
https://leetcode.com/contest/biweekly-contest-31/problems/minimum-number-of-increments-on-subarrays-to-form-a-target-array/
Accumulate the difference between neigbour numbers, this can be done in O(N), four lines of code.

I'll share the solutions on the [blog](https://helloacm.com) in more details soon.

Although the contest has ended, you can try to participate on the virtual contest.

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Every little helps! I hope this helps!


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