Problem
Take every contiguous window of span digits and multiply its digits. Return the largest product. Leading zeros are ordinary digits; a window containing zero has product zero. Do not reorder or skip digits.
Implement largest_adjacent_digit_product(digits, span).
Input
digits: The digit sequence, including any leading zeros.
span: The exact number of adjacent digits in a window.
Output
Return the greatest product over all windows of this width.
Constraints
1 ≤ digit-string length ≤ 100,000. Characters are 0…9. 1 ≤ span ≤ min(18, length). All products fit signed 64-bit.
Examples
Input:
span = 2
digits = "23405"
Expected output:
expected = 12Input:
long long span = 2;
std::string digits = "23405";
Expected output:
long long expected = 12;Input:
long span = 2;
string digits = "23405";
Expected output:
long expected = 12;Explanation
The windows 23, 34, 40, and 05 have products 6, 12, 0, and 0. The largest is 12.
Input:
span = 3
digits = "102"
Expected output:
expected = 0Input:
long long span = 3;
std::string digits = "102";
Expected output:
long long expected = 0;Input:
long span = 3;
string digits = "102";
Expected output:
long expected = 0;Explanation
There is only one width-three window. It contains zero, so 1 × 0 × 2 = 0.
How to approach it
Try on your own first, then open one hint at a time.
Hint 1
A zero inside a window forces that product to zero, so only contiguous nonzero stretches can contribute to the maximum.
Hint 2
Use a sliding window or track products across runs of digits to avoid recomputing every span from scratch.
Hint 3
Watch the exact span requirement: leading zeros count as digits, and if span exceeds a nonzero block, the product is zero.
Expected complexity
O(n) time, O(1) extra space
References
This challenge is adapted for CodeUtility. Follow the statement and constraints above.