BCG X tends to care about how you think as much as code quality, so I’d prep for a mix rather than pure Leetcode. Are you targeting junior or mid level? I’ve seen a common pattern for similar software engineering interviews be a live coding round on data structures and algorithms plus a conversational behavioral chat, sometimes with a light system design discussion. I usually practice stories with a simple situation action result format and keep answers around 90 seconds, then run a timed mock with Beyz coding assistant after pulling a few prompts from the IQB interview question bank. Talking through your approach as you code helps a ton fwiw.

First round was a coding test and Second round was technical round - both these rounds went fine. Third round (technical case interview) was extremely average. It was supposed to be taken on a portal but the portal did not have option to code in Flask. So the interviewer made me code in my local desktop. Setting up my project and database itself took an hour. The interviewer expected me to code the full stack case in 30 mins?! I didnt even get to showcase my Angular skills which was my strong point. Received rejection the next day after technical case interview.