Plus One — LeetCode 66 Python Solution

The problem

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.

Example

Input

digits = [1,2,3]

Output

[1,2,4]

Explanation

The array represents the integer 123.

Python solution

class Solution:
    def plusOne(self, digits: List[int]) -> List[int]:
        n = len(digits)
        for i in range(n - 1, -1, -1):
            digits[i] += 1
            digits[i] %= 10
            if digits[i] != 0:
                return digits
        return [1] + digits

Complexity

Pattern: Math and Number Theory

Find the closed form, the invariant, or the modular identity — and skip the loop entirely. LeetCode 66. Plus One is filed here on both counts: the reference solution below belongs to the algorithm family this hub collects, and LeetCode tags it Math.

The math and number theory guide has the Python template for the pattern and the 485 LeetCode problems that use it.

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