 # Problem Name: Minion AND Range; Problem Code: MINIAND

I was trying to solve the problem, which deals with executing Q queries on a sequence of +ve numbers, and each query is of type [L, R], where I need to find whether bitwise-AND of A[L\ldots R] will be EVEN or ODD.
The solution which I implemented gives TLE.
How can I optimise the solution for an AC, and as it is query problem, either you do some pre-computation in order to find the answer to queries in constant time or use a data-structure to answer the query in less than O(n) time as the query is related to ranges.

As I have already seen some of the submission, and I can only understand the most of them have used prefix sum method, so please don’t only give me the source-code, I really appreciate it, if someone can explain the logic in plain English or can provide a well-documented code.

Peace 1 Like

Just check if an even number exists inbetween by prefix sums.

1 Like

You can use a prefix array to count the parity, but i simply used a segment tree I know it’s too much😂but i had the template ready… Segment Tree won’t let u down if u implement it correctly

@just1star Can you tell me how to use prefix array, I know prefix array but in this problem context, how to use it, Do I need to store the count of even numbers upto a[i]?

@anon73162591 Segment tree is one of the option which will comes first in mind when dealing with range queries, How did you use the segment tree?

Peace The problem involves checking whether a range of elements has a bitwise and (&)= even or not. we know that :
even & even=even
even & odd=even
odd & odd = odd
now we know that even a single occurance of a even number will make the whole array (or range)even.
now the task is to find if ranges contain or not a even number for this we can use a prefix array and store the number of even number till each index.
atlast check for if even[r]-even[r]!=0 then even else false.
we can use an prefix array for same

3 Likes

I made a segment tree to return me the bitwise AND between ranges… I just took that and checked if it was even or odd…

Solved the problem, here is my Solution, thanks for valuable suggestions.

Peace 