plus-one.py

"""
# https://github.com/kamyu104/LeetCode/blob/master/Python/plus-one.py

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

The digits are stored such that the most significant digit is at the head of the list, and each element in the array contain a single digit.

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

Example 1:

Input: [1,2,3]
Output: [1,2,4]
Explanation: The array represents the integer 123.
Example 2:

Input: [4,3,2,1]
Output: [4,3,2,2]
Explanation: The array represents the integer 4321.

""" 

# V0
# NOTE : Notice the index of inverse loop  : range(len(a)-1, -1, -1)
# a = ['a', 'b', 'c']
# for i in range(len(a)-1, -1, -1):
#     print (a[i])
# c
# b
# a
class Solution(object):
    def plusOne(self, digits):
        """
        :type digits: List[int]
        :rtype: List[int]
        """
        plus = 1
        for i in range(len(digits)-1, -1, -1):
            if digits[i] + plus > 9:
                digits[i] = 0
                plus = 1
            else:
                digits[i] = digits[i] + plus
                plus = 0
        if plus == 1:
            digits.insert(0, 1)
        return digits

# V0'
# IDEA : array -> string -> int -> string 
class Solution:
    def plusOne(self, digits):
        digits_ = [str(i) for i in digits]
        d = int(''.join(digits_))
        d += 1 
        return list(str(d))

# V1 
# https://blog.csdn.net/coder_orz/article/details/51583916
class Solution(object):
    def plusOne(self, digits):
        """
        :type digits: List[int]
        :rtype: List[int]
        """
        plus = 1
        for i in range(len(digits)-1, -1, -1):
            if digits[i] + plus > 9:
                digits[i] = 0
                plus = 1
            else:
                digits[i] = digits[i] + plus
                plus = 0
        if plus == 1:
            digits.insert(0, 1)
        return digits

### Test case : dev

# V1' 
# https://blog.csdn.net/coder_orz/article/details/51583916
class Solution(object):
    def plusOne(self, digits):
        """
        :type digits: List[int]
        :rtype: List[int]
        """
        for i in range(len(digits)-1, -1, -1):
            if digits[i] < 9:
                digits[i] = digits[i] + 1
                return digits
            else:
                digits[i] = 0
        digits.insert(0, 1)
        return digits

# V2 
# Time:  O(n)
# Space: O(1)
class Solution(object):
    def plusOne(self, digits):
        """
        :type digits: List[int]
        :rtype: List[int]
        """
        for i in reversed(range(len(digits))):
            if digits[i] == 9:
                digits[i] = 0
            else:
                digits[i] += 1
                return digits
        digits[0] = 1
        digits.append(0)
        return digits

# Time:  O(n)
# Space: O(n)
class Solution2(object):
    def plusOne(self, digits):
        """
        :type digits: List[int]
        :rtype: List[int]
        """
        result = digits[::-1]
        carry = 1
        for i in range(len(result)):
            result[i] += carry
            carry, result[i] = divmod(result[i], 10)
        if carry:
            result.append(carry)
        return result[::-1]