66.Plus One

Tags: [list], [array]

Com: {g}

Link: https://leetcode.com/problems/plus-one/\#/description

Given a non-negative integer represented as a non-empty array of digits, plus one to the integer.

You may assume the integer do not contain any leading zero, except the number 0 itself.

The digits are stored such that the most significant digit is at the head of the list.

Solution:

class Solution(object):
    def plusOne(self, digits):
        """
        :type digits: List[int]
        :rtype: List[int]
        """
        if not digits:
            raise ValueError('the input is invalid')

        carry = 1
        for i in xrange(len(digits) - 1, -1, -1):
            tmp = digits[i] + carry
            digits[i] = tmp % 10
            carry = tmp / 10

        if carry > 0:
            digits.insert(0, carry)

        return digits

Revelation:

• Here we assume the interviewer tell us that we can modify he given input.
• In Python, list.insert(position, val).

Note:

• Time complexity = O(n), n is the number of elements in the given array.
• Space complexity = O(1).