66. Plus One

Description

Given a non-negative integer represented as a non-empty array of digits, plus one to the integer.

You may assume the integer do not contain any leading zero, except the number 0 itself.

The digits are stored such that the most significant digit is at the head of the list.

Solution

Iteration

public class Solution {
    public int[] plusOne(int[] digits) {
        int carry = 1;
        
        for (int i = digits.length - 1; i >= 0; --i) {
            int val = digits[i] + carry;
            digits[i] = val % 10;
            carry = val / 10;
        }
        
        if (carry == 0) return digits;
        
        int[] newDigits = new int[digits.length + 1];
        newDigits[0] = 1;   // it's enough because all the rest digits are zero!
        return newDigits;
    }
}