LeetCode-066：Plus One

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题目：

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.

题意：

数组所有元素组成一个整数，求这个整数+1后的值

思路：

从个位（末尾元素）开始做加法运算，需特别注意的是：如果最后一位是9，那么就要进位（最后一个元素改成0，倒二个元素+1.。。。继续下去）~还有比如整数是999，则要在数组最前面插入一个1

Code：

class Solution {
public:
    vector<int> plusOne(vector<int>& digits) {
        int n=digits.size();
        for (int i=n-1;i>=0;i--) {
            if (digits[i]==9) digits[i] = 0;
            else {
                digits[i] += 1;
                return digits;
            }
        }
        if (digits.front()==0) digits.insert(digits.begin(),1);
        return digits;
    }
};