Is Largest Even Number easy or hard?

Largest Even Number is generally considered an easy problem. The core insight is recognizing that only the final digit determines whether the number is even. Once that constraint is handled, constructing the maximum value becomes straightforward.

Largest Even Number Python/Java solution

In Python or Java, iterate through the string to count digits, choose the smallest even digit for the last position, and build the remaining digits in descending order. Python commonly uses lists or collections.Counter, while Java uses an int[10] array for digit frequencies.

How to solve Largest Even Number in O(n)?

Use a digit frequency array of size 10. Scan the string once to count occurrences of each digit. Choose the smallest even digit for the final position, reduce its frequency, then rebuild the number by appending digits from 9 down to 0 based on remaining counts. This avoids sorting and runs in linear time.

What is the best approach for Largest Even Number?

The greedy digit placement approach is the most practical. Identify the smallest even digit to place at the last position, then arrange the remaining digits in descending order to maximize the number. This ensures the number remains even while keeping larger digits in higher place values. Time complexity is O(n log n) with sorting, or O(n) using digit counting.

Is Largest Even Number asked at Google/Amazon/Meta?

Variants of digit rearrangement and greedy number construction appear in interviews at large tech companies. The problem tests understanding of digit constraints, greedy ordering, and efficient string or array manipulation rather than advanced data structures.

What data structure is used in Largest Even Number?

Most solutions use simple arrays or strings. The optimal approach uses a fixed-size frequency array (size 10) to count digits. This allows efficient reconstruction of the number without sorting.

What is the time complexity of Largest Even Number?

The optimal solution runs in O(n) time using a frequency count of digits from 0 to 9. After counting digits, reconstruct the number in descending order and place the chosen even digit at the end. A simpler implementation using sorting runs in O(n log n) time.

Description Hints 2 Solution Video 2:37

3798. Largest Even Number

Easy68.5% acceptance

You are given a string s consisting only of the characters '1' and '2'.

You may delete any number of characters from s without changing the order of the remaining characters.

Return the largest possible resultant string that represents an even integer. If there is no such string, return the empty string "".

Example 1:

Input: s = "1112"

Output: "1112"

Explanation:

The string already represents the largest possible even number, so no deletions are needed.

Example 2:

Input: s = "221"

Output: "22"

Explanation:

Deleting '1' results in the largest possible even number which is equal to 22.

Example 3:

Input: s = "1"

Output: ""

Explanation:

There is no way to get an even number.

Constraints:

1 <= s.length <= 100
s consists only of the characters '1' and '2'.

Topics

String

Hints open one at a time

Hint 1

A number ending with '1' is odd.

Hint 2

Find the last '2' in s. If none, return "". Otherwise return the prefix up to and including that '2'.

2:37

Still stuck?Read the written solution, or watch a walkthrough.

Open solution

LanguageLoading editor…

1class Solution:
2    def largestEven(self, s: str) -> str:
3        

Starter codePython 3Spaces: 4

Examples

Case 1Case 2Case 3

Input

"1112"

Input

"221"

Input

"1"

Your code is saved on this device.Solution