Coding Interviews can be hard. Knowing algorithms and data structures is required, but not enough. You need to practice. A lot. Solving problems on your own is a good start, but practicing online with a real person as an interviewer is much better.
Sometimes it is useful to edit multiple places in the file at once, which can save you precious time and increase your productivity. IntelliJ IDEA supports having multiple cursors at once, meaning you can type and edit at multiple locations at the same time.