How do you solve Second Largest Digit in a String on LeetCode?

Second Largest Digit in a String (LeetCode #1796) can be solved using Brute Force or Optimal Solution. The optimal approach is Optimal Solution with O(n) time complexity and O(n) space complexity. Key insight: Using a set helps to automatically handle duplicates.

What is the brute force solution for Second Largest Digit in a String?

The brute force approach for Second Largest Digit in a String is Brute Force, with O(n²) time complexity and O(n) space complexity. The brute-force approach involves checking every character in the string to find all the digits, then sorting them to find the second largest. It's straightforward but inefficient. The optimal Optimal Solution approach improves this to O(n).

What algorithm or data structure is used to solve Second Largest Digit in a String?

Second Largest Digit in a String uses the following concepts: Hash Table, String. The recommended patterns to study are: Hash Map, Array.

What are the interview tips for Second Largest Digit in a String?

Always consider edge cases, like strings without digits. Explain your thought process clearly while coding. Optimize your solution after the brute-force approach.

What are common mistakes when solving Second Largest Digit in a String?

Not handling the case where there are fewer than two distinct digits. Confusing character comparison with integer comparison.

#1796

Second Largest Digit in a String

Easy

Hash TableStringHash MapArray

LeetCode ↗

Approaches

Brute ForceOptimal

Complexity Comparison

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

💡

Intuition

Time O(n)Space O(n)

The optimal approach uses a set to collect digits while iterating through the string, then directly finds the second largest without sorting. This is more efficient.

⚙️

Algorithm

4 steps

1Step 1: Initialize a set to collect unique digits.
2Step 2: Iterate through each character in the string. If it's a digit, add it to the set.
3Step 3: Convert the set to a list and check its size. If less than 2, return -1.
4Step 4: Find the maximum digit, remove it, and find the new maximum, which is the second largest.

solution.py12 lines

1# Full working Python code
2
3def second_largest_digit(s):
4    digits = set()
5    for char in s:
6        if char.isdigit():
7            digits.add(int(char))
8    if len(digits) < 2:
9        return -1
10    max_digit = max(digits)
11    digits.remove(max_digit)
12    return max(digits)

ℹ

Complexity note: The time complexity is O(n) because we only iterate through the string once and perform constant-time operations with the set. The space complexity is O(n) for storing the digits.

1Using a set helps to automatically handle duplicates.
2Finding the maximum and then the second maximum is efficient.

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