题目网址: https://www.puzzleup.com/2021/
https://www.puzzleup.com/2021/puzzle/?5
答题时限: ９月30日７ＰＭ－比赛结束（约11月９日）
加分时限: ９月30日７ＰＭ－10月５日６：５９ＰＭ
答对可得基本分１００分。答案可上传５次，每改１次答案从基本分扣２０分。　
比赛期间内可随时上传答案，加分时限内答对第ｎ天加（６－ｎ）分　 　　 　　
另依题目的难易有额外加分（如有８０％的人这题答错，答对者加８０分）　　
◆GRID PAINTING
You have 3 different colors to paint the squares of a 3x3 grid.
-The total number of squares to be painted is 5.
-Each painted square must be adjacent (horizontally or vertically) to another
painted square.
-Adjacent squares (horizontally or vertically) should be painted in different
colors.
How many different ways can this task be done?
Notes:
-All three colors must be used.
-Disconnected groups of connected squares are allowed.
将三个颜色涂在一个 3x3 格子中。
- 恰好涂五个格子。
- 任何涂色格子需要水平或垂直相邻另一个涂色格子。
- 而如此相邻的两个涂色格子需要不同颜色。
试问这样的涂色法有多少种？
注:
- 三种颜色均要使用。
- 允许有两群连续的格子彼此不相邻。
If the problem was asked for 2x2 grid and 2 different colors, and the number
of squares to paint was 3, the answer would be 8.
若此问题改问 2x2 格子，两种颜色，涂三格，则答案为 8:
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