#leetcode# Plus One

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

The digits are stored such that the most significant digit is at the head of the list, and each element in the array contain a single digit.

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

Example 1:

Input: [1,2,3]
Output: [1,2,4]
Explanation: The array represents the integer 123.

Example 2:

Input: [4,3,2,1]
Output: [4,3,2,2]
Explanation: The array represents the integer 4321.

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 很简单的一个题， 但是写得好的还是看得出功力的。。

下面两个版本是我没经过什么思考写的和discuss中比较好的solution的比较，小学生和大学生的区别。

做题多了可能看见同质化的问题就都想套用常见套路，缺少了思考。这个题还是比较适合去当面试热身题的

小学生：

class Solution {
    public int[] plusOne(int[] digits) {
        int carry = 1;
        for (int i = digits.length - 1; i >= 0; i--) {
            int num = digits[i] + carry;
            digits[i] = num % 10;
            carry = num / 10;
        }
        int[] res = null;
        if (carry == 1) {
            res = new int[digits.length + 1];
            res[0] = 1;
            for(int j = 1; j < res.length; j++){
                res[j] = digits[j - 1];
            }
        }else{
            res = digits;
        }
        return res;
    }
}

大学生：

class Solution {
    public int[] plusOne(int[] digits) {
        
        int n = digits.length;
        for(int i=n-1; i>=0; i--) {
            if(digits[i] < 9) {
                digits[i]++;
                return digits;   //  You can early terminate the loop !
            }

            digits[i] = 0;
        }

        int[] newNumber = new int [n+1];
        newNumber[0] = 1;           // If this case happens, the following positions are all zero !

        return newNumber;
    }
}