How do you solve Find the Sum of Encrypted Integers on LeetCode?

Find the Sum of Encrypted Integers (LeetCode #3079) can be solved using Brute Force or Optimal Solution. The optimal approach is Optimal Solution with O(n) time complexity and O(1) space complexity. Key insight: The encrypted number can be derived directly from the maximum digit and the number of digits in the original number.

What is the brute force solution for Find the Sum of Encrypted Integers?

The brute force approach for Find the Sum of Encrypted Integers is Brute Force, with O(n²) time complexity and O(1) space complexity. We can replace each digit of a number with the largest digit in that number. This can be done by converting the number to a string, finding the maximum digit, and then constructing the new number. Finally, we sum all the encrypted numbers. The optimal Optimal Solution approach improves this to O(n).

What algorithm or data structure is used to solve Find the Sum of Encrypted Integers?

Find the Sum of Encrypted Integers uses the following concepts: Array, Math. The recommended patterns to study are: Array, Math.

What are the interview tips for Find the Sum of Encrypted Integers?

Always start with a simple approach to demonstrate your thought process, even if it's not optimal. Explain your reasoning clearly as you transition to more optimal solutions. Practice dry runs of your code with sample inputs to ensure you understand the flow.

What are common mistakes when solving Find the Sum of Encrypted Integers?

Students often forget to handle the conversion between characters and integers when finding the maximum digit. Some may attempt to use complex data structures unnecessarily instead of simple arithmetic.

#3079

Find the Sum of Encrypted Integers

Easy

ArrayMathArrayMath

LeetCode ↗

Approaches

Brute ForceOptimal

Complexity Comparison

	Brute Force	Optimal Solution★
Time	O(n²)	O(n)
Space	O(1)	O(1)

💡

Intuition

Time O(n)Space O(1)

Instead of constructing the encrypted number by string manipulation, we can directly calculate the sum using the largest digit and the number of digits in each number. This avoids unnecessary string operations and speeds up the process.

⚙️

Algorithm

6 steps

1Step 1: Initialize a variable to hold the total sum.
2Step 2: For each number in the input array, find the maximum digit.
3Step 3: Determine the number of digits in the number.
4Step 4: Calculate the encrypted number directly as maxDigit * (10^numberOfDigits - 1) / 9.
5Step 5: Add the encrypted number to the total sum.
6Step 6: Return the total sum.

solution.py13 lines

1# Full working Python code
2
3def encrypt_sum_optimal(nums):
4    total_sum = 0
5    for num in nums:
6        max_digit = max(int(d) for d in str(num))
7        number_of_digits = len(str(num))
8        encrypted_num = max_digit * (10**number_of_digits - 1) // 9
9        total_sum += encrypted_num
10    return total_sum
11
12# Example usage
13print(encrypt_sum_optimal([10, 21, 31]))  # Output: 66

ℹ

Complexity note: The time complexity is O(n) because we only iterate through the array once, and for each number, we find the maximum digit and calculate the encrypted number in constant time. This is much more efficient than the brute force approach.

1The encrypted number can be derived directly from the maximum digit and the number of digits in the original number.
2Understanding how to manipulate numbers and strings efficiently is key to optimizing solutions.

Solutions and explanations are original Tejav content. Problem titles © LeetCode — use the LeetCode button above for the full problem statement.