Is Number of Digit One easy or hard?

Number of Digit One is labeled Hard because the pattern is not obvious from the problem statement. The brute force approach is simple but inefficient, while the optimal O(log n) solution requires recognizing digit cycles and applying mathematical reasoning.

Number of Digit One Python/Java solution

Most implementations follow the same digit-position formula. Use a loop that multiplies a factor by 10 each iteration, derive higher/current/lower values from n, and update the result accordingly. The logic is identical across Python, Java, C++, and other languages.

How to solve Number of Digit One in O(log n)?

Iterate through digit positions using a factor variable (1, 10, 100...). For each position, compute the higher digits, the current digit, and the lower digits. Based on whether the current digit is 0, 1, or greater than 1, calculate how many ones appear in that position and accumulate the total.

What is the best approach for Number of Digit One?

The best approach counts contributions from each digit position independently. By analyzing the higher, current, and lower digits around a position (ones, tens, hundreds), you can compute how many times '1' appears at that position. This reduces the complexity to O(log n) time with O(1) space.

Is Number of Digit One asked at Google/Amazon/Meta?

Digit counting and range‑based math problems similar to Number of Digit One frequently appear in interviews at companies like Google, Amazon, and Meta. They test number pattern recognition, mathematical reasoning, and the ability to optimize beyond brute force solutions.

What data structure is used in Number of Digit One?

No complex data structure is required. The optimal solution relies on arithmetic operations and digit decomposition. Variables representing higher digits, the current digit, and lower digits are enough to compute the count.

What is the time complexity of Number of Digit One?

The optimal digit-position counting solution runs in O(log n) time because it processes each decimal digit once. Space complexity remains O(1) since only a few integer variables are required. A brute force approach that checks every number takes O(n log n).