Add One to an Integer Stored as Digits Without ArrayList

Problem Statement

Given an array of digits representing a non-negative integer, increment the integer by one and return the resulting array. The digits are stored such that the most significant digit is at the index 0.

Because the input array represents a fixed-size integer, if the increment causes an overflow (e.g., [9, 9] becomes [1, 0, 0]), you must return a new array with the appropriate size. You are not permitted to convert the array to a primitive integer type or use dynamic collection classes like ArrayList or List to build the result; you must manage the array memory explicitly.

Function Signature

int[] plusOne(int[] digits)

Constraints

• 1 <= digits.length <= 1000
• 0 <= digits[i] <= 9
• The integer does not contain leading zeros unless the integer is exactly [0].

Examples

Example 1: Input: digits = [1, 2, 3] Output: [1, 2, 4] Explanation: 123 + 1 = 124.

Example 2: Input: digits = [9, 9] Output: [1, 0, 0] Explanation: 99 + 1 = 100.

Edge Cases

• Single digit array (e.g., [9] -> [1, 0], [0] -> [1]).
• Array with trailing nines (e.g., [8, 9, 9] -> [9, 0, 0]).