Complexity of Jelly-No and Hanano games with various constraints

TL;DR

This paper investigates the computational complexity of Jelly-No and Hanano games, establishing new PSPACE-completeness results for Jelly-No with multiple colours and black jellies, and NP-hardness for fixed board dimensions.

Contribution

It proves Jelly-No is PSPACE-complete with multiple colours and black jellies, and NP-hard for fixed board sizes, extending previous complexity results.

Findings

Jelly-No is PSPACE-complete with unbounded colours.

Jelly-No with black jellies is PSPACE-complete even for one colour.

One-colour Jelly-No and Hanano are NP-hard on fixed board dimensions.

Abstract

This work shows new results on the complexity of games Jelly-No and Hanano with various constraints on the size of the board and number of colours. Hanano and Jelly-No are one-player, 2D side-view puzzle games with a dynamic board consisting of coloured, movable blocks disposed on platforms. These blocks can be moved by the player and are subject to gravity. Both games, created by Qrostar and available online, somehow vary in their gameplay, but the goal is always to move the coloured blocks in order to reach a specific configuration and make them interact with each other or with other elements of the game. In Jelly-No the goal is to merge all blocks of the same colour, which happens when they make contact. In Hanano the goal is to make all the coloured blocks bloom by making contact with flowers that have the same colour. Jelly-No was proven by Chao Yang to be NP-complete under the restriction that all movable blocks have the same colour and NP-hard for more colours. Hanano was proven by Michael C. Chavrimootoo to be PSPACE-complete under the restriction that all movable blocks have the same colour. However, the question of PSPACE-completeness for Jelly-No with more than one colours was left open. In this paper, we settle this question, proving that Jelly-No is PSPACE-complete with an unbounded number of colours. We further show that, if we allow black jellies (that is, jellies that cannot and do not need to merge), the game is PSPACE-complete even for one colour. We further show that one-colour Jelly-No and Hanano remain NP-hard even if the width or the height of the board are constants.