我是阿副，不是阿母!

假設鐵環都在 A 鐵柱上 後來都移道 C 鐵柱

步驟     鐵環號碼     原鐵柱→後來的鐵柱

1              1

A              →           B

2              2

A              →           C

3              1

B              →           C

4              3

A              →           B

5              1

C              →           A

6               2

C              →           B

7               1

A              →            B

8               4

A              →            C

9               1

B              →            C

10             2

B              →             A

11             1

C              →             A

12             3

B               →            C

13              1

A               →             B

14              2

A               →             C

15              1

B               →              C