Add One To Number

Given a non-negative number represented as an array of digits,

add 1 to the number ( increment the number represented by the digits ).

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

Example:

If the vector has [1, 2, 3]

the returned vector should be [1, 2, 4]

as 123 + 1 = 124.

 

NOTE: Certain things are intentionally left unclear in this question which you should practice asking the interviewer.
For example, for this problem, following are some good questions to ask :

• Q : Can the input have 0’s before the most significant digit. Or in other words, is 0 1 2 3 a valid input?

• A : For the purpose of this question, YES

• Q : Can the output have 0’s before the most significant digit? Or in other words, is 0 1 2 4 a valid output?
• A : For the purpose of this question, NO. Even if the input has zeroes before the most significant digit.

My solution:

class Solution:
    # @param A : list of integers
    # @return a list of integers
    def plusOne(self, A):
        size = len(A)
        results = list()
        sum = 0
        for i in range(size):
            if i == 0 and A[i] == 0 and size > 1:
                pass
            # results.append(A[i])
            if i > 0:
                sum *= 10
            sum += A[i]
            if i == size - 1:
                sum += 1
                str_result = str(sum)

        for i in range(len(str_result)):
            results.append(int(str_result[i]))

        return results

Good solutions:

Although you should not solve it this way as you should know the actual implementation
but this is an easier alternative for python guys.

1. class Solution:
2. 1.

3. # @param A : list of integers
   

4. # @return a list of integers
   

5. def plusOne(self,A):
   

6.     s = ''.join(map(str, A))
   

7.     res = int(s)
   

8.     res+=1
   

9.     res = [int(x) for x in str(res)]
   

10.     return res

2. return str(int(''.join(map(str, A)))+1)