LeetCode 3798: Largest Even Number

Meta Data

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Difficulty: easy First Attempt: 2026-01-04

• Submissions: Accepted (first try)

Approach

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The string has only 1s and 2s, and a number is even when its last digit is 2. More digits mean a larger number, so delete only what is necessary: strip the trailing 1s, and the rest is the largest even number. All 1s gives the empty string.

My Solution

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class Solution:
    def largestEven(self, s: str) -> str:
        return s.rstrip("1")

I originally deleted them one at a time in a while loop; rstrip does the same.

Complexity

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Time O(n), space O(n).

Mistakes to Avoid

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• Deleting middle digits only makes the number shorter and smaller; only the end matters.

Interview Explanation

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Parity depends only on the last digit, and keeping more digits is larger, so I just strip the trailing 1s. Time O(n).