Finding the largest sequence of identical digits using recursive function (c++) [closed] - c++

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I need to find the largest sequence of identical digits in a given integer using a recursive function.
For example:
input: "2221", output: 3
input: "2223333", output: 4
input: "222333", output: 3
For some reason the code sometimes works correctly and sometimes it doesn't. when I input "1112" then it gives me the correct output (3), but when I input "1111555", I expected to get the output 4, but instead got 6.
Also, I can't change the parameters that the function receives so if someone knows how can I insert the parameters inside the function instead of outside (if I insert them inside the function then the output I receive is always 0)
I'd really appreciate the help so thank you in advance :)
My code:
int currentLength = 0, maxLength = 0;
int currentDigit = -1;
int maxSequence(int num)
{
if (num <= 0)
return maxLength;
int digit = num % 10;
if (digit == currentDigit) {
maxLength= 1 + maxSequence(num / 10);
}
else {
currentDigit = digit;
if (maxLength > 1)
{
maxLength = 0;
}
else
{
maxLength = 1;
}
return maxSequence(num / 10);
}
}

Answer 1

Recursion and mutable global variables is a nasty combination.
You can add the parameters to a different function and call that instead.
Something like this:
// Since you can't use std::max.
int max(int a, int b) { return a > b ? a : b; }
int maxSequenceHelper(int number, int last, int length, int maximum)
{
int digit = number % 10;
if (digit == last)
{
length += 1;
maximum = max(length, maximum);
}
else
{
length = 1;
}
return number < 10
? maximum
: maxSequenceHelper(number / 10, digit, length, maximum);
}
int maxSequence(int number)
{
return maxSequenceHelper(number / 10, number % 10, 1, 1);
}
And here is a version without any assignments, making it slightly easier to reason about:
int maxSequenceHelper(int number, int last, int length, int maximum)
{
const int digit = number % 10;
const int new_length = digit == last ? length + 1 : 1;
const int new_maximum = max(new_length, maximum);
return number < 10
? new_maximum
: maxSequenceHelper(number / 10, digit, new_length, new_maximum);
}