[LeetCode July Challange]Day6-Plus One

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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solution

time complexity : O(n)
space complexity : O(n)

class Solution {
public:
    vector<int> plusOne(vector<int>& digits) {
        int carry = 1;
        for (int i=digits.size()-1; i>=0; --i) {
            digits[i] += carry;
            carry = digits[i] / 10;
            digits[i] %= 10;
        }
        if (carry) digits.insert(digits.begin(), carry);
        return digits;
    }
};

此題不可將陣列轉為數值，+1後再轉為陣列，這種資料結構通常是應用在數值超出一般數值資料結構能表示的範圍。
因此只能從最低位元(陣列最後一個元素)開始，一個一個慢慢往前進位。最後再檢查是否有進位多一位，再插入陣列的第一個位置即可。