Is Maximum 69 Number easy or hard?

Maximum 69 Number is classified as an Easy problem on LeetCode with a high acceptance rate around 84%. It mainly tests basic greedy thinking and simple digit processing rather than complex data structures or algorithms.

Maximum 69 Number Python/Java solution

In Python or Java, convert the number to a string, scan characters from left to right, replace the first '6' with '9', and convert back to an integer. The logic is identical across languages and runs in O(n) time with straightforward implementation.

How to solve Maximum 69 Number in O(n)?

Convert the number to a string and iterate from the leftmost digit. When you encounter the first 6, replace it with 9 and stop scanning. This single pass guarantees O(n) time and ensures the largest possible increase because the change occurs at the highest place value.

What is the best approach for Maximum 69 Number?

The greedy approach is the best solution. Scan the digits from left to right and replace the first occurrence of 6 with 9. Because higher place values contribute more to the number, flipping the earliest 6 produces the maximum increase. This runs in O(n) time where n is the number of digits.

Is Maximum 69 Number asked at Google/Amazon/Meta?

Maximum 69 Number is considered an easy-level interview warm‑up. Variations of digit manipulation and greedy reasoning appear in coding screens at companies like Amazon and Google. The problem tests understanding of place value and simple greedy optimization.

What data structure is used in Maximum 69 Number?

Most implementations convert the integer into a string or character array to easily modify digits. This allows direct replacement of the first 6 with 9 during iteration. A mathematical approach can also solve it using division and modulo operations without extra data structures.

What is the time complexity of Maximum 69 Number?

Both common solutions run in O(n) time, where n is the number of digits in the number. The algorithm scans the digits once to find the first 6. Space complexity is O(n) for the string-based greedy solution or O(1) for the mathematical digit manipulation approach.

Description Hints 2 Solution Video 7:21

1323. Maximum 69 Number

Easy84.5% acceptance7 companies

You are given a positive integer num consisting only of digits 6 and 9.

Return the maximum number you can get by changing at most one digit (6 becomes 9, and 9 becomes 6).

Example 1:

Input: num = 9669
Output: 9969
Explanation: 
Changing the first digit results in 6669.
Changing the second digit results in 9969.
Changing the third digit results in 9699.
Changing the fourth digit results in 9666.
The maximum number is 9969.

Example 2:

Input: num = 9996
Output: 9999
Explanation: Changing the last digit 6 to 9 results in the maximum number.

Example 3:

Input: num = 9999
Output: 9999
Explanation: It is better not to apply any change.

Constraints:

1 <= num <= 10⁴
num consists of only 6 and 9 digits.

Asked at 7 companies

Hrt HSBC

Google Amazon Microsoft Meta Bloomberg

Topics

Greedy Math

Hints open one at a time

Hint 1

Convert the number in an array of its digits.

Hint 2

Brute force on every digit to get the maximum number.

7:21

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

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2    def maximum69Number (self, num: int) -> int:
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