Implement atoi (string to integer conversion)

Problem Implement a function to convert a numeric string into an integer. Input: a string s consisting only of digits 0-9 Output: the corresponding base-10 integer For this problem, ignore signs, whitespace, and overflow (the input is guaranteed to be a valid non-negative integer string). Constraints 1 <= len(s) <= 1e5 Examples Input: "123" Output: 123 Input: "0" Output: 0 Requirements Time complexity: O(n) Do not call built-in string-to-integer conversion (e.g., int(s)). Example Input 123 Output 123