# 66. Plus One
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 = [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].

## 解題思路
判斷最後一位數是否小於9
是:直接+1
否:改位數+1為0，並往前一位數繼續判斷，如全部位數皆為0，則最左位數為1。

## 圖解

input: 456
out: 45(6+1) = 457

input: 99
out: 1(9+1)(9+1) = 100

## Java Code

public class Solution {
    public int[] plusOne(int[] digits) {
        int n = digits.length;
        for (int i = digits.length - 1; i >= 0; --i) {
            if (digits[i] < 9) {
                ++digits[i];
                return digits;
            }
            digits[i] = 0;
        }
        int[] res = new int[n + 1];
        res[0] = 1;
        return res;
    }
}