the author of HUNGER GAMES, Suzanne Collins, has already stated she had never heard of BATTLE ROYALE before she wrote the HUNGER GAMES trilogy, that it was not based on BATTLE ROYALE, but she got the idea by watching reality TV shows and TV coverage of the Iraq war.
There are only a finite number of plots in fiction, and in dystopian fiction (which I write) there are even fewer. Many novel plots are similar, and in most cases, it is purely coincidental. My own work-in-progress has some similarities to HUNGER GAMES and Marie Lu's LEGEND novel series. (btw, a highly recommended dystopian novel series.) It just happens that way sometimes.
“The only way to deal with an unfree world is to become so absolutely free that your very existence is an act of rebellion.”
― Albert Camus