I'm working in C# with a four-digit random number and a list of special numbers, such as 1225 and 2112. I want to detect whether the random number is exactly one digit different from any special number. For example, 1925 should match 1225 because changing the 9 to a 2 makes it special. The different digit could appear in any position and could be replaced with any other digit. If multiple special numbers are one digit away, I may want to choose the one with the highest priority. I considered using minimax to try possible replacements, but that seems unnecessarily expensive. What would be a simpler and efficient approach?
3 Answers
Minimax is unnecessary for this. Loop through the special numbers and compare them with the current value one digit at a time. Count how many positions differ, and stop checking as soon as the count exceeds one. A candidate is valid when exactly one position differs. If several candidates qualify, choose the one with the best priority score. With four-digit values, this requires very little work.
You can also generate every possible one-digit replacement and check whether the result exists in a HashSet of special numbers. For a four-digit number, there are only 4 × 9 possible replacements, so this is still tiny and avoids scanning a large list. A HashSet gives fast lookups. Make sure to treat the value as a four-character string if leading zeroes are allowed.
A direct comparison against each special number is probably the clearest solution. For example, 1925 compared with 1225 differs only at the second position, so it matches. Comparing it with a number that differs in two or more positions should fail. You don’t need to identify the replacement separately—the matching special number already tells you what the digit should become.
If multiple special numbers differ by one digit, the result depends on their order unless you add an explicit priority. It would be better to compare all matching candidates and return the highest-scoring one instead of immediately returning the first match.