Hello, Can anyone explain idea to solve E. Lucky Array problem. I tried to understand from editorial but I'm finding difficult to understand. Problem Link:E. Lucky Array

Problem Description: Petya loves lucky numbers. Everybody knows that lucky numbers are positive integers whose decimal representation contains only the lucky digits 4 and 7. For example, numbers 47, 744, 4 are lucky and 5, 17, 467 are not.

Petya has an array consisting of n numbers. He wants to perform m operations of two types:

add l r d — add an integer d to all elements whose indexes belong to the interval from l to r, inclusive (1 ≤ l ≤ r ≤ n, 1 ≤ d ≤ 10^4);

count l r — find and print on the screen how many lucky numbers there are among elements with indexes that belong to the interval from l to r inclusive (1 ≤ l ≤ r ≤ n).

Each lucky number should be counted as many times as it appears in the interval. Petya has a list of all operations. The operations are such that after all additions the array won't have numbers that would exceed 10^4. Help Petya write a program that would perform these operations.

It's beyond your scope. Don't be over smart by solving such difficult problems. Solve problem of your level.

At least I'm using real account, not a fake account like you to comment.

I agree that the editorial is poorly written, I will try to solve it today and describe my solution here, potentially better.

Thank you.

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