Hudson-river-trading C++ New Graduate Tech Phone Screen Interview Experience

I recently had an interview for a C++ new grad position at HRT. The interview lasted 30 minutes; we introduced ourselves and then it quickly began. The question was: Design a game. The board has 9x9 d

I recently had an interview for a C++ new grad position at HRT. The interview lasted 30 minutes; we introduced ourselves and then it quickly began. The question was: Design a game. The board has 9x9 dots, and sticks can be placed to connect adjacent dots. The top-left dot's coordinates are (1, 1), and the bottom-right dot's coordinates are (9, 9). The rules are that players take turns placing sticks on the board. Sticks must connect two adjacent dots. The game ends when a 1x1 square appears on the board, and the player who made the last move wins. Each round's moves need to print the board to std out. After writing the code, the interviewer asked me to run the program, reading the coordinates of the sticks placed by both players from std in. For example, inputting 1 1 1 2 means the player connected points (1, 1) and (1, 2). This question has a high degree of freedom; there were no test cases. The question itself is simple, but there are many things to implement. The most troublesome part was probably how to detect game ends. Ultimately, I used a brute-force search across the entire board (using a double for-loop to check if any of the 81 possible square locations were filled out). I successfully completed the code, but didn't have time to implement error checking, such as catching the error when two sticks are placed in the same space. I guess that's why I failed. Sigh, based on previous interview experiences, I thought it would be a C++ cliché interview, but it turned out to be a coding interview. Posting this here is just to accumulate good karma, please give me some points, thank you!