66. Plus One

Alen Alex · February 12, 2026

LeetCode Link: 66. Plus One
Language: C#

Problem Statement

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.

Solution

public class Solution 
{
    public int[] PlusOne(int[] digits) 
    {
        digits[digits.Length - 1]++;

        for (int i=digits.Length - 2; i>=0; i--)
        {
            if (digits[i+1] == 10)
            {
                digits[i+1] = 0;
                digits[i]++;
            }
        }

        int offset = (digits[0] == 10 ? 1 : 0);
        var n2 = new int[digits.Length + offset];

        if (digits[0] == 10)
        {
            digits[0] = 0;
            n2[0] = 1;
        }

        for (int i=0; i<digits.Length; i++)
        {
            n2[i+offset] = digits[i];
        }

        return n2;
    }
}

Twitter, Facebook