【LeetCode】(66)Plus One (Easy)

题目

Plus One

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Question Solution 

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.

解析

主要是考虑99999这种情况。如果你先把他转成整数，再转回来，那就大错特错了，因为会！溢！出！

从末尾处理起就好了，要考虑999这种加一后长度增加的情况

class Solution {public:    vector<int> plusOne(vector<int>& digits) {     vector<int> ret; if (digits[digits.size()-1] == 9) { digits[digits.size()-1] = 10; }        else        {             digits[digits.size()-1]++;        } for (int i = digits.size()-1; i>0; i--) { if (digits[i] == 10) { digits[i] = 0; digits[i-1]++; }  } if (digits[0] == 10) { digits[0] = 0; digits.insert(digits.begin(),1); } return digits;    }};

大神代码如下

// LeetCode, Plus One// 时间复杂度O(n)，空间复杂度O(1)class Solution {public:vector<int> plusOne(vector<int> &digits) {    add(digits, 1);    return digits;}private:// 0 <= digit <= 9void add(vector<int> &digits, int digit) {    int c = digit; // carry, 进位    for_each(digits.rbegin(), digits.rend(), [&c](int &d)    {        d += c;        c = d / 10;        d %= 10;    });    if (c > 0) digits.insert(digits.begin(), 1);    }};