Plus One

问题描述

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

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

解决思路

检查digits数组中是否全是9，如果全是，直接返回手动计算的结果即可；

否则，数组遍历做加法。 

程序

public class Solution {
    public int[] plusOne(int[] digits) {
        if (digits == null || digits.length == 0) {
            return new int[0];
        }
        
        boolean isLonger = checkDigits(digits);
        int len = digits.length;
        
        if (isLonger) {
            int[] res = new int[len + 1];
            res[0] = 1;
            return res;
        }
        
        int[] res = new int[len];
        int i = len - 1;
        int c = 1;
        while (i >= 0) {
            int s = digits[i] + c;
            int d = s % 10;
            c = s / 10;
            res[i] = d;
            --i;
        }
        
        return res;
    }
    
    private boolean checkDigits(int[] digits) {
        for (int d: digits) {
            if (d != 9) {
                return false;
            }
        }
        return true;
    }
}