LeetCode | Plus One

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.

//思想類似於前兩天的add binary與add two numbers
//數組中，高位在左，低位在右，故反向遍歷並維護進位
public class Solution {
    public int[] plusOne(int[] digits) {
        
        if(digits==null || digits.length==0){
            return null;
        }
        
        int carry = 1;     //在第一次循環時，充當one的角色，以後作爲進位標誌位
        int index = digits.length - 1;
        
        while(index >= 0){
            int temp = digits[index] + carry; 
            int newDigit = temp % 10;
            carry = temp / 10;
            
            digits[index] = newDigit;
            index--;
        }
        
        if(carry > 0){       //因僅僅加1，若此時還有進位，則原數組畢爲9999..形式
            int[] result = new int[digits.length+1];
            result[0] = 1;   //新建個擴充數組，且首位爲1即可
            return result;
        }else{
            return digits;
        }
        
    }
}