本题和 A147 是重题。 思路 用四维动态规划，按题意模拟即可。 状态转移 dp[x1 mod 2][y1][x2][y2]=max⁡{dp[(x1−1) mod 2][y1][x2−1][y2],dp[(x1−1) mod 2][y1][x2][y2−1],dp[x1 mod 2][y1−1][x2−1][y2],dp[x1 mod 2][y1−1][x2][y2−1]dp\left[x_{1} \bmod 2\right]\left[y_{1}\right]\left[x_{2}\right]\left[y_{2}\right]=\max \left\{\begin{array}{l} dp\left[\left(x_{1}-1\right) \bmod 2\right]\left[y_{1}\right]\left[x_{2}-1\right]\left[y_{2}\right], \\ dp\left[\left(x_{1}-1\right) \bmod 2\right]\left[y_{1}\right]\left[x_{2}\right]\left[y_{2}-1\right], \\ dp\left[x_{1} \bmod 2\right]\left[y_{1}-1\right]\left[x_{2}-1\right]\left[y_{2}\right], \\ dp\left[x_{1} \bmod 2\right]\left[y_{1}-1\right]\left[x_{2}\right]\left[y_{2}-1\right] \end{array}\right. dp[x1 mod2][y1 ][x2 ][y2 ]=max⎩⎨⎧ dp[(x1 −1)mod2][y1 ][x2 −1][y2 ],dp[(x1 −1)mod2][y1 ][x2 ][y2 −1],dp[x1 mod2][y1 −1][x2 −1][y2 ],dp[x1 mod2][y1 −1][x2 ][y2 −1] 代码