Abstract / Summary

Given an encrypted integer string, return the sum of the actual values represented by each encrypted string in the list.

Note

The full problem description, including helpful examples, can be found on LeetCode.

This problem is ranked as

and has an acceptance rate of about 75% (80k+ submissions).

Every single line of code was written by me, 100% from scratch, between August 2023 and August 2024.
However, two years later I set up this website and used various AI tools to generate most of the walkthrough / explanations below.

See this dedicated page for more details.

Overview

The provided implementation defines a single method sumOfEncryptedInt inside a Solution class. The method receives a list of integers, transforms each integer into a derived numeric value, and returns the aggregate of those values. The transformation follows a specific rule: for each integer, the length of its decimal representation is multiplied by the largest digit present in that representation, and the product is interpreted as a decimal integer. The final result is the sum of all such products across the input list.

Key Steps

The core logic is expressed as a generator expression inside the built-in sum function. The outermost operation aggregates the per-element results:

return sum(int(len(str(n)) * max(str(n))) for n in nums)

The generator iterates over each element n in the input list nums. For each n, the following sub-steps are performed:

1. Convert the integer to its string representation to expose individual digits:

   str_n = str(n)

2. Determine the number of characters in that string, which corresponds to the digit count of the original integer:

   digit_count = len(str_n)

3. Identify the maximum character (digit) in the string. Because the characters are numeric, the lexical maximum coincides with the numeric maximum:

   max_digit_char = max(str_n)

4. Multiply the digit count by the maximum digit character. The multiplication occurs between an integer (digit_count) and a string (max_digit_char). Python implicitly converts the string to an integer during the multiplication, yielding an integer product:

   product = digit_count * max_digit_char

5. Convert the product to an integer explicitly, ensuring the generator yields an integer value for the summation:

   encrypted_value = int(product)

The generator yields encrypted_value for each n, and sum aggregates them into the final result.

Edge Cases Handled

The implementation gracefully handles several edge conditions without additional branching:

• Zero and single-digit numbers: For n = 0 or any single-digit integer, len(str(n)) evaluates to 1, and max(str(n)) yields the digit itself. The product therefore equals the digit, and the conversion to int preserves the correct value.

• Negative integers: When n is negative, str(n) includes a leading minus sign. The len function counts this sign as a character, and max(str(n)) will consider the minus sign ('-') as having a lower lexical value than any digit. Consequently, the maximum digit remains the highest numeric character, while the length includes the sign. This behavior yields a deterministic product that reflects the sign’s presence in the length count.

• Large integers: The conversion to string and the subsequent operations are linear in the number of digits, allowing the method to process arbitrarily large integers as long as they fit in memory. The final integer conversion (int(...)) correctly interprets the product regardless of magnitude.

• Empty input list: If nums is empty, the generator produces no values, and sum returns the neutral element 0. This matches the mathematical expectation for the sum over an empty collection.

Performance Optimizations Observed

The code leverages Python’s built-in functions and generator expression to minimize overhead:

• Generator expression: By using a generator rather than constructing an intermediate list, the implementation avoids allocating additional memory proportional to the input size. Each element is processed and summed on the fly.

• String operations: Converting the integer to a string once per element enables both the length and maximum digit calculations without repeated conversions. The max function operates directly on the string, which is efficient for short digit sequences.

• Implicit type coercion: Multiplying an integer by a single-character string triggers Python’s internal conversion of the character to an integer, eliminating the need for an explicit int(max_digit_char) call before multiplication. The final int(...) ensures the result is an integer for the summation, but the intermediate multiplication remains lightweight.

• Built-in sum: Utilizing the highly optimized C implementation of sum provides fast aggregation compared to a manual loop in pure Python.

These choices collectively produce a concise solution that processes each input element in a single pass with minimal temporary storage and leverages the interpreter’s optimized primitives.

Imagine you have a box full of number blocks. This code acts like a special machine that plays a game with those blocks. First, the machine looks at each number in the box one by one. For every number, it checks how many digits are sitting side by side and remembers that length. Then, it finds the biggest digit hiding inside that same number. The machine turns that biggest digit into a long row of identical numbers by repeating it as many times as the length of the original number. Finally, the machine gathers all the new numbers it made, adds them all together into one big pile, and sets the total aside on the table.

Several LLMs ranked my code quality on a scale from 1 (very poor) to 10 (outstanding):

not analyzed yet

I wrote a basic crawler to find other solutions to that problem.
Obviously, I did that after I solved the problem myself.

In general, AlgoMonster and WalkCCC solutions are high-quality and always worth a look.
I haven't checked most of the other solutions, but they might be helpful as well.

And of course, the LeetCode forum is always a good place (or even the best) to look for alternative approaches.

(click on a column header to sort the table)

	author
author	solutions
www	AlgoMonster	Java				C++	Python	TS
	WalkCCC	Java				C++	Python
	leetcode.ca	Java		Go		C++	Python	TS
	Progiez	Java				C++	Python
github	charles-wangkai	Java
	fsq					C++
	JoshCrozier		JS
	muhammadfarhankt			Go
	shreymehul				C#
	varunu28	Java
AlgoMonster	C++, Python, Java, TypeScript
WalkCCC	C++, Python, Java
leetcode.ca	C++, Go, Java, Python, TypeScript
Progiez	C++, Java, Python
charles-wangkai	Java
fsq	C++
JoshCrozier	JavaScript
muhammadfarhankt	Go
shreymehul	C#
varunu28	Java

There are a few extra pages giving you some insights into my setup:

• Tech Stack - my development environment and tools
• AI - how AI helped me create this website (NOT solving the problems)
• Progress - progression over time
• Quality - code quality