Is Monotone Increasing Digits easy or hard?

Monotone Increasing Digits is classified as a medium difficulty problem. The challenge comes from recognizing the greedy correction strategy and handling cascading digit decreases when the monotone condition breaks.

Monotone Increasing Digits Python/Java solution

Implementations typically convert the number to a string or digit list, perform the greedy adjustment, then rebuild the final number. The same logic works across Python, Java, C++, C#, and JavaScript since it only relies on digit traversal and basic arithmetic operations.

How to solve Monotone Increasing Digits in O(n)?

Treat the number as a digit array and scan for the first violation where digit[i] < digit[i-1]. Decrement the previous digit and propagate the correction backward if needed. After fixing the prefix, set all remaining digits to 9 to maximize the number while maintaining the monotone condition.

What is the best approach for Monotone Increasing Digits?

The greedy digit-adjustment approach is the optimal method. Convert the number into digits, detect where the monotone order breaks, decrement the previous digit, and fill the remaining suffix with 9s. This guarantees the largest number less than or equal to n with non‑decreasing digits and runs in O(d) time where d is the number of digits.

Is Monotone Increasing Digits asked at Google/Amazon/Meta?

Monotone Increasing Digits represents a common greedy digit manipulation pattern often discussed in coding interviews. Variants of this style of problem appear in interviews at large tech companies such as Google, Amazon, and Meta, especially when testing greedy reasoning and number manipulation skills.

What data structure is used in Monotone Increasing Digits?

Most solutions convert the integer into a string or array of digits so each position can be modified individually. The algorithm then performs simple index-based iteration and updates, making the digit array the primary structure used during computation.

What is the time complexity of Monotone Increasing Digits?

The optimal greedy solution runs in O(d) time and O(d) space, where d is the number of digits in the input number. Each digit is inspected and possibly adjusted once, making the algorithm extremely efficient compared to brute force approaches.

Description Hints 1 Solution Video 18:08

738. Monotone Increasing Digits

Q: What is the best approach for Monotone Increasing Digits?

The greedy digit-adjustment approach is the optimal method. Convert the number into digits, detect where the monotone order breaks, decrement the previous digit, and fill the remaining suffix with 9s. This guarantees the largest number less than or equal to n with non‑decreasing digits and runs in O(d) time where d is the number of digits.

Q: Is Monotone Increasing Digits asked at Google/Amazon/Meta?

Monotone Increasing Digits represents a common greedy digit manipulation pattern often discussed in coding interviews. Variants of this style of problem appear in interviews at large tech companies such as Google, Amazon, and Meta, especially when testing greedy reasoning and number manipulation skills.

Q: What data structure is used in Monotone Increasing Digits?

Most solutions convert the integer into a string or array of digits so each position can be modified individually. The algorithm then performs simple index-based iteration and updates, making the digit array the primary structure used during computation.

Q: What is the time complexity of Monotone Increasing Digits?

The optimal greedy solution runs in O(d) time and O(d) space, where d is the number of digits in the input number. Each digit is inspected and possibly adjusted once, making the algorithm extremely efficient compared to brute force approaches.

Medium50.1% acceptance3 companies

An integer has monotone increasing digits if and only if each pair of adjacent digits x and y satisfy x <= y.

Given an integer n, return the largest number that is less than or equal to n with monotone increasing digits.

Example 1:

Input: n = 10
Output: 9

Example 2:

Input: n = 1234
Output: 1234

Example 3:

Input: n = 332
Output: 299

Constraints:

0 <= n <= 10⁹

Asked at 3 companies

Amazon Goldman Sachs

Google

Topics

Greedy Math

Hints open one at a time

Hint 1

Build the answer digit by digit, adding the largest possible one that would make the number still less than or equal to N.

18:08

Still stuck?Read 2 approaches, or watch a walkthrough.

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