Project Euler/8

Problem 8 on Project Euler: https://projecteuler.net/problem=8

Question

We are given a 1000 digit number.

The four adjacent digits in the 1000-digit number that have the greatest product are 9 × 9 × 8 × 9 = 5832.

We are asked: find the thirteen adjacent digits in the 1000-digit number that have the greatest product. What is the value of this product?

Approach

The approach here is similar to the palindrome product problem: we run through the 1000 digit number, extracting 13-digit strings, for a total of 1000 - 13 = 987 different numbers. These should be sorted in order of greatest to smallest digits, and the maximum kept.

Note that the key to this problem is not in the problem itself, but in the format of how the numbers are stored the largest digit that you'll find will be just a bit above 2^32, so if you are using a 32 bit representation you can get deceptively okay-looking numbers that are actually incorrect.