LeetCode 66. Plus One

Description

https://leetcode.com/problems/plus-one/

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

Example 4:

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.

Explanation

Use sum and carry to track the effect when the given digits plusing by one.

Python Solution

class Solution:
    def plusOne(self, digits: List[int]) -> List[int]:
        result = []
        
        carry = 0        
        i = len(digits) - 1
        
        while (i >= 0):
            sum = digits[i] + carry
            if i == len(digits) - 1:
                sum = sum + 1
            
            digit = sum % 10
            carry = sum // 10
            
            result.insert(0, digit)
            i = i - 1
        
        if carry > 0:
            result.insert(0, carry)            
        
        return result
  • Time complexity: O(N)
  • Space complexity: O(N)

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