I am majoring in theoretical ecology at the University of Tokyo. I am scheduled to graduate from the current MSc program in March 2020, and I am planning to get in a Ph.D. program (outside Japan, due to financial and other problems). My interests are mathematical/computational biology/ecology, combinatorics, graph theory, exponential algorithms, etc.
Currently, my biggest concern is that I have no CS degrees, or even something related to CS. I graduated from the University of Tokyo in ecology BSc. However, I have achievements and contributions in competitive programming area more than average (How 'more than average'? This is my list Link).
Is it possible for non-CS students with competition achievements like me to get in CS PhD program to research algorithms? How are the chances? Does it depend on schools or region? I have no one to ask about it because almost all the redcoders are CS or mathematics major, and especially in Japan, very few people apply for PhD program overseas. Any advice (other than common advice you can find on the top search result of "how to get in phd" or something) is more than welcome ;)
P.S. Recently I resumed posting videos related to algorithms and programming contest techniques to Youtube. Take a look if you are interested. Link