How do you solve Largest Even Number on LeetCode?

Largest Even Number (LeetCode #3798) 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: An even number must end with '2'.

What is the time complexity of Largest Even Number?

The optimal solution for Largest Even Number runs in O(n) time and uses O(n) space. Finding the last index and slicing the string is linear in time.

What is the brute force solution for Largest Even Number?

The brute force approach for Largest Even Number is Brute Force, with O(n²) time complexity and O(1) space complexity. Generate all possible substrings and check if they represent an even number. This is inefficient but straightforward. The optimal Optimal Solution approach improves this to O(n).

What algorithm or data structure is used to solve Largest Even Number?

Largest Even Number uses the following concepts: String. The recommended patterns to study are: String Manipulation, Greedy Algorithms.

What are the interview tips for Largest Even Number?

Clarify edge cases (e.g., no '2'). Discuss time complexity upfront. Explain your thought process clearly.

What are common mistakes when solving Largest Even Number?

Forgetting to check if '2' exists. Returning the wrong substring length.

#3798

Largest Even Number

Easy

StringString ManipulationGreedy Algorithms

LeetCode ↗

Approaches

Brute ForceOptimal

Complexity Comparison

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

💡

Intuition

Time O(n)Space O(n)

Find the last '2' in the string and return the prefix up to that point. This guarantees the largest even number.

⚙️

Algorithm

3 steps

1Step 1: Find the last occurrence of '2' in s.
2Step 2: If found, return the substring from the start to that index (inclusive).
3Step 3: If not found, return an empty string.

solution.py3 lines

1def largest_even_number(s):
2    last_two = s.rfind('2')
3    return s[:last_two + 1] if last_two != -1 else ""

ℹ

Complexity note: Finding the last index and slicing the string is linear in time.

1An even number must end with '2'.
2The largest number is formed by keeping the leftmost digits intact.

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