Starting state: there are 4 stacks: - Stack 1: green block (alone) - Stack 2: blue block (alone) - Stack 3: orange block (alone) - Stack 4: purple block, red block, from bottom to top Ending state: there are 4 stacks: - Stack 1: blue block (alone) - Stack 2: purple block (alone) - Stack 3: green block (alone) - Stack 4: orange block, red block, from bottom to top