A Cards (贪心)
http://blog.youkuaiyun.com/baidu_19306071/article/details/52005372
B Cells Not Under Attack (模拟)
http://blog.youkuaiyun.com/baidu_19306071/article/details/52005417
C They Are Everywhere(尺取/双指针)
http://blog.youkuaiyun.com/baidu_19306071/article/details/52005454
D As Fast As Possible(数学推公式)
E Connecting Universities (DFS)
http://blog.youkuaiyun.com/baidu_19306071/article/details/52005557