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C D E1 E2(E2 思维 有意思的一个模型） F 交互题，根据叉积的性质找凸包。先一直找更逆时针方向的直线，找出相邻的一个点，其他点根据面积从小到大排序，对于每个点与1构成的向量，再与比它高的点比较顺逆时针方向即可得到，连左或连右。