Is Latest Time by Replacing Hidden Digits easy or hard?

Latest Time by Replacing Hidden Digits is classified as an Easy problem. The challenge lies in understanding the constraints of the 24‑hour clock and applying greedy logic to choose the maximum valid digit for each position.

Latest Time by Replacing Hidden Digits Python/Java solution

In Python or Java, convert the string to a mutable character array and replace '?' based on position rules. Apply greedy checks for the hour digits (00–23) and minute digits (00–59). After replacements, convert the array back to a string and return the resulting time.

How to solve Latest Time by Replacing Hidden Digits in O(1)?

Scan the time string and greedily replace each '?' with the largest digit allowed by the 24‑hour format. The first hour digit can be '2' or '1' depending on the second digit, the second hour digit depends on whether the first is '2', the first minute digit can be '5', and the last minute digit can be '9'. Because the string size never changes, the solution runs in constant time.

What is the best approach for Latest Time by Replacing Hidden Digits?

The most efficient approach is greedy conditional replacement. For each '?' digit, choose the maximum value that still forms a valid 24‑hour time. Because the string length is fixed (HH:MM), the algorithm runs in O(1) time and O(1) space while guaranteeing the latest valid result.

Is Latest Time by Replacing Hidden Digits asked at Google/Amazon/Meta?

Problems involving time formatting and greedy digit replacement appear frequently in interviews at large tech companies. While this exact question is most commonly seen in coding practice platforms, the pattern of constraint‑based string manipulation is relevant to interviews at companies like Amazon and Google.

What data structure is used in Latest Time by Replacing Hidden Digits?

The solution mainly uses string or character array manipulation. No complex data structures are required; the logic relies on conditional checks and greedy digit selection based on the constraints of a valid 24‑hour time.

What is the time complexity of Latest Time by Replacing Hidden Digits?

The time complexity is O(1). The input always has exactly five characters (HH:MM), so the algorithm performs a constant number of checks and replacements regardless of input. Space complexity is also O(1) since the modification happens directly on the string or a small character array.

Description Hints 2 Solution Video 10:29

1736. Latest Time by Replacing Hidden Digits

Easy43.7% acceptance1 company

You are given a string time in the form of hh:mm, where some of the digits in the string are hidden (represented by ?).

The valid times are those inclusively between 00:00 and 23:59.

Return the latest valid time you can get from time by replacing the hidden digits.

Example 1:

Input: time = "2?:?0"
Output: "23:50"
Explanation: The latest hour beginning with the digit '2' is 23 and the latest minute ending with the digit '0' is 50.

Example 2:

Input: time = "0?:3?"
Output: "09:39"

Example 3:

Input: time = "1?:22"
Output: "19:22"

Constraints:

time is in the format hh:mm.
It is guaranteed that you can produce a valid time from the given string.

Asked at 1 company

Google

Topics

Greedy String

Hints open one at a time

Hint 1

Trying out all possible solutions from biggest to smallest would fit in the time limit.

Hint 2

To check if the solution is okay, you need to find out if it's valid and matches every character

10:29

Still stuck?Read 3 approaches, or watch a walkthrough.

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