Recursive Digit Sum Discussions |

2 weeks ago+ 0 comments

Python 3 solution

Initially I tried expanding the string n by k multiple:

full_integer = n * k

This lead to runtime error in 4 hidden cases.

Instead, summing all digits in n then multiplying by k solves the runtime issue.

def int_to_int_arr(integer):
    return list(map(int, str(integer)))

def sum_array(n):
    if len(n) != 1:
        new_int = sum(n)
        int_arr = int_to_int_arr(new_int)
        return sum_array(int_arr)
    else:
        # One digit left in integer
        return n[0]

def superDigit(n, k):
    # Cast n string to int array
    int_arr = list(map(int, n))
    
    # Multiply sum by k
    sum_multiple = sum(int_arr) * k
    
    # Cast sum multiple to int array
    int_arr = int_to_int_arr(sum_multiple)
    return sum_array(int_arr)

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