Plus One

Description

You are given a large integer represented as an integer array digits, where each digits[i] is the ith digit of the integer. The digits are ordered from most significant to least significant in left-to-right order. The large integer does not contain any leading 0‘s.

Increment the large integer by one and return the resulting array of digits.

Example 1:

Input: digits = [1,2,3] Output: [1,2,4] Explanation: The array represents the integer 123. Incrementing by one gives 123 + 1 = 124. Thus, the result should be [1,2,4].

Example 2:

Input: digits = [4,3,2,1] Output: [4,3,2,2] Explanation: The array represents the integer 4321. Incrementing by one gives 4321 + 1 = 4322. Thus, the result should be [4,3,2,2].

Example 3:

Input: digits = [9] Output: [1,0] Explanation: The array represents the integer 9. Incrementing by one gives 9 + 1 = 10. Thus, the result should be [1,0].

Constraints:

• 1 <= digits.length <= 100
• 0 <= digits[i] <= 9
• digits does not contain any leading 0‘s.

Code

Time Complexity: $O(n)$, Space Complexity: $O(1)$

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

Source

• Plus One - LeetCode