How do you solve Largest 3-Same-Digit Number in String on LeetCode?

Largest 3-Same-Digit Number in String (LeetCode #2264) 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: Checking for the largest good integer first allows for early termination.

What is the brute force solution for Largest 3-Same-Digit Number in String?

The brute force approach for Largest 3-Same-Digit Number in String is Brute Force, with O(n²) time complexity and O(1) space complexity. We will check every possible substring of length 3 in the given string. If it consists of the same digit, we will track the maximum found. This method is straightforward but inefficient for larger strings. The optimal Optimal Solution approach improves this to O(n).

What algorithm or data structure is used to solve Largest 3-Same-Digit Number in String?

Largest 3-Same-Digit Number in String uses the following concepts: String. The recommended patterns to study are: Hash Map, Array.

What are the interview tips for Largest 3-Same-Digit Number in String?

Always clarify the problem constraints and edge cases. Think about the efficiency of your approach and explain your reasoning. Be prepared to discuss the trade-offs between different methods.

What are common mistakes when solving Largest 3-Same-Digit Number in String?

Not considering leading zeros as valid good integers. Overlooking the fact that the first found good integer in the optimal approach is guaranteed to be the largest.

#2264

Largest 3-Same-Digit Number in String

Easy

StringHash MapArray

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 checking every substring, we can directly check for the largest possible good integers from '999' to '000'. This way, we can stop as soon as we find the first match, making the solution efficient.

⚙️

Algorithm

4 steps

1Step 1: Loop through digits from '9' to '0'.
2Step 2: For each digit, create a substring of three of that digit (e.g., '999', '888').
3Step 3: Check if this substring exists in the original string. If it does, return it immediately as it will be the largest.
4Step 4: If no good integer is found after the loop, return an empty string.

solution.py6 lines

1def largestGoodInteger(num):
2    for digit in range(9, -1, -1):
3        good_integer = str(digit) * 3
4        if good_integer in num:
5            return good_integer
6    return ""

ℹ

Complexity note: The time complexity is O(n) because we only scan the string once for each of the 10 digits. The space complexity is O(1) since we are not using any additional space that grows with input size.

1Checking for the largest good integer first allows for early termination.
2Using a direct search for fixed patterns is more efficient than checking all substrings.

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