LeetCode-66. 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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参考代码：

1.最坏情况下，时间复杂度为O（2N）。digits的insert函数要执行一遍数组。

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

优化：

1.最坏情况下时间复杂度O（N）。

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