In Facebook phone interview, they try to get you solve and code two problems. How about the onsite coding round? Is the expectation same? Coding two problem might be possible if they are medium problems. For medium problems you will probably try to get to coding as soon as you can. But for hard problems, you probably should take time, think through, work out an example. Should I try to guess first if the given problem is hard or medium and based on that change my strategy?