Remove Digit From Number to Maximize Result

Remove Digit From Number to Maximize Result

What is this problem about?

The Remove Digit From Number to Maximize Result interview question gives you a large number represented as a string and a specific digit character. You must remove exactly one occurrence of that digit from the number string such that the resulting number is as large as possible. The result should also be returned as a string. This problem tests greedy decision-making in the context of string manipulation.

Why is this asked in interviews?

This question is asked at Microsoft, Meta, Amazon, Google, and Bloomberg because it combines string traversal with greedy thinking. It seems simple at first glance but has a subtle edge case: there may be multiple occurrences of the digit to remove, and picking the wrong one gives a suboptimal answer. Candidates who understand when to apply greedy enumeration and when to fall back to the last occurrence demonstrate solid problem-solving skills.

Algorithmic pattern used

The pattern is greedy enumeration. Scan through the number string from left to right. When you encounter the target digit, check if the character immediately after it is larger. If so, removing the current occurrence will produce the largest number — do it immediately. If you finish scanning and never found such a position (meaning the digit is at the end or always followed by an equal or smaller digit), remove the last occurrence of the digit.

Example explanation

Number: "2319", digit: '3'.

• At index 1, the digit is '3'. The next character is '1', which is smaller than '3', so removing here would shrink the number. Keep scanning.
• But wait — scanning forward: after '3' comes '1'. Since '1' < '3', skip.
• Apply fallback: remove the last (and only) '3' at index 1. Result: "219".

Now try number "1231", digit '1':

• At index 0, next char is '2' which is larger — remove index 0. Result: "231". This is the maximum.

Common mistakes candidates make

• Always removing the first occurrence without checking the following character.
• Forgetting the fallback case: if no occurrence is followed by a strictly larger digit, you must remove the last occurrence.
• Incorrectly handling strings where the digit appears only once at the very end.
• Not returning the result as a string, or returning it with a leading zero.

Interview preparation tip

For the Remove Digit From Number to Maximize Result coding problem, the enumeration and greedy interview pattern applies cleanly here. Write two passes mentally: one forward pass looking for the ideal removal point, and a fallback to the last occurrence. Practice on edge cases where all occurrences of the digit are at the end of the string. Interviewers at Google and Bloomberg appreciate candidates who explicitly state their greedy criterion — "remove the leftmost occurrence followed by a larger digit" — before coding.