66. One Plus

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.

Solution:

先后两遍扫描,
从右开始向左计算, 当前位置满10修改成0, 左位置+1.
若首位10, vector尾部添加0, 首位修改成0, 中间添0.

class Solution {
 public:
  vector<int> plusOne(vector<int> &digits) {
    int n = digits.size();
    int i = n; digits[--i]++;
    while (digits[i] == 10 && i > 0) {
      digits[i] = 0;
      digits[--i]++;
    }
    if (digits[0] == 10) {
      digits.push_back(0);
      digits[0] = 1;
      for (int j = 1; j < n; j++) digits[j] = 0;
    }

    return digits;
  }
};