A warm-up problem is illustrated below: Suppose that like repels like at a distance of two, and the only strand types are aqua, blue, crimson and dark yellow.
英
美
- 下图是一道暖身题:我们将条件改成,假设在三个相邻的圆环内,其颜色是互斥的,而且只使用浅绿、蓝、深红、土黄四种颜色。