For the problem 6.2 in v 1.4.4 Incrementing Big Integer, What if,
“The array of digits could also encode a negative decimal number”,
Then in that case, increment by one must move the number down in the opposite direction on the number line than on the wrong direction which would be indeed a decrement operation for negative number.
Assuming that a negative big decimal is a valid legal input, it would then break the posted solution.
Even if negative big decimal input is not expected or not a valid legal input the variant posed an interesting exercise to the brain.
Posting my solution to handle the negative numbers as well. (I took the freedom to alter the method signature a little bit to avoid code and input format clumsiness. To avoid input like [-5, 2] etc ). It is written in python.
def increment(L, sign):
i = len(L)-1 #start with the last element
while(i >=0 ):
if sign == 'P':
new_val = L[i]+1
if new_val <= 9:
L[i] = new_val
break
else:
L[i] = 0
i = i - 1
continue
elif sign == 'N':
new_val = L[i] - 1
if new_val < 0:
L[i] = 9
i = i - 1
continue
else:
L[i] = new_val
break
if L[0] == 0 and sign == 'P': #handle for MSB updated to 10 case.
L = [1] + L
if L[0] == 9 and sign == 'N': #handle for [1, 'N'] case.
L = [0]
return L
Valid inputs for sign are ‘P’ for positive and ‘N’ for negative decimals.
Examples:
a = [1,0,0]
increment(a, ‘N’) --> Should output [0, 9, 9]
a = [1,0,0]
increment(a, ‘P’) --> Should output [1, 0, 1]
