PlusOne.java

package by.andd3dfx.numeric;

/**
 * <pre>
 * <a href="https://leetcode.com/problems/plus-one/">Task description</a>
 *
 * You are given a large integer represented as an integer array digits, where each digits[i] is the ith digit
 * of the integer. The digits are ordered from most significant to least significant in left-to-right order.
 * The large integer does not contain any leading 0's.
 *
 * Increment the large integer by one and return the resulting array of digits.
 *
 * Example 1:
 *
 * Input: digits = [1,2,3]
 * Output: [1,2,4]
 * Explanation: The array represents the integer 123.
 * Incrementing by one gives 123 + 1 = 124.
 * Thus, the result should be [1,2,4].
 *
 * Example 2:
 *
 * Input: digits = [4,3,2,1]
 * Output: [4,3,2,2]
 * Explanation: The array represents the integer 4321.
 * Incrementing by one gives 4321 + 1 = 4322.
 * Thus, the result should be [4,3,2,2].
 *
 * Example 3:
 *
 * Input: digits = [9]
 * Output: [1,0]
 * Explanation: The array represents the integer 9.
 * Incrementing by one gives 9 + 1 = 10.
 * Thus, the result should be [1,0].
 * </pre>
 *
 * @see <a href="https://youtu.be/qk6lt-lC2Nc">Video solution</a>
 */
public class PlusOne {

    public static int[] plusOne(int[] digits) {
        if (digits.length == 0) {
            throw new IllegalArgumentException("Array shouldn't be empty!");
        }

        var pos = digits.length - 1;
        digits[pos]++;

        while (pos >= 0) {
            if (digits[pos] < 10) {
                return digits;
            }

            digits[pos] = 0;
            if (pos == 0) {
                var result = new int[digits.length + 1];
                System.arraycopy(digits, 0, result, 1, digits.length);
                result[0] = 1;
                return result;
            }
            digits[pos - 1]++;
            pos--;
        }
        return digits;
    }
}