题解：https://frankchenfu.blog.luogu.org/solution-p2679
其中f[i][j][p][1]=f[i−1][j−1][p][1]+f[i−1][j−1][p−1][0]+f[i−1][j−1][p−1][1]f[i][j][p][1]=f[i−1][j−1][p][1]+f[i−1][j−1][p−1][0]+f[i−1][j−1][p−1][1]f[i][j][p][1]=f[i−1][j−1][p][1]+f[i−1][j−1][p−1][0]+f[i−1][j−1][p−1][1]怎么解释？ .
