Is Valid Number easy or hard?

Valid Number is classified as a Hard problem because of the large number of edge cases. The logic itself is straightforward once broken into rules, but ensuring all valid formats and rejecting invalid ones requires careful state tracking.

How to solve Valid Number in O(n)?

Traverse the string once while maintaining boolean flags such as seenDigit, seenDot, and seenExponent. Allow digits anywhere, allow a decimal only once before an exponent, and ensure an exponent appears only after at least one digit. Sign characters are valid only at the start or immediately after an exponent. This single-pass validation guarantees O(n) time complexity.

Valid Number Python or Java solution?

Both Python and Java solutions typically implement a single-pass parser with boolean flags. Python solutions may also use the re module for regex matching, while Java commonly uses character iteration with conditions. In both languages the optimal complexity remains O(n) time and O(1) space.

What is the best approach for Valid Number?

The iterative parsing approach is generally the best solution. It scans the string once while tracking rules for digits, decimal points, signs, and exponents using simple flags. This method runs in O(n) time and O(1) space and clearly demonstrates understanding of string parsing logic, which interviewers typically expect.

What data structure is used in Valid Number?

The problem mainly uses string traversal with a few boolean state variables. No complex data structures are required. The algorithm relies on parsing rules that track whether digits, decimal points, or exponent markers have already appeared.

What is the time complexity of Valid Number?

Both common solutions run in O(n) time where n is the length of the string. Each character is processed once either by the regex engine or a manual parsing loop. Space complexity is O(1) because only a few flags or a compiled pattern are stored.

Is Valid Number asked at Google, Amazon, or Meta?

Valid Number is a classic string parsing problem that has appeared in interviews at companies like Google, Amazon, and Meta. It tests careful handling of edge cases and state-based validation rather than heavy data structures or algorithms.

Description Solution Video 11:33

65. Valid Number

Hard23.3% acceptance7 companies

Given a string s, return whether s is a valid number.

For example, all the following are valid numbers: "2", "0089", "-0.1", "+3.14", "4.", "-.9", "2e10", "-90E3", "3e+7", "+6e-1", "53.5e93", "-123.456e789", while the following are not valid numbers: "abc", "1a", "1e", "e3", "99e2.5", "--6", "-+3", "95a54e53".

Formally, a valid number is defined using one of the following definitions: