Tarjan

Hawk-and-Chicken (HDU - 3639) 题面 Kids in kindergarten enjoy playing a game called Hawk-and-Chicken. But there always exists a big problem: every kid in this game want to play the role of Hawk. So the teacher came up with an idea: Vote. Every child have some nice handkerchiefs, and if he/she think someone is suitable for the role of Hawk, he/she gives a handkerchief to this kid, which means this kid who is given the handkerchief win the support. Note the support can be transmitted. Kids who get the most supports win in the vote and able to play the role of Hawk.(A note:if A can win support from B(A != B) A can win only one support from B in any case the number of the supports transmitted from B to A are many. And A can’t win the support from himself in any case. If two or more kids own the same number of support from others, we treat all of them as winner. Here’s a sample: 3 kids A, B and C, A gives a handkerchief to B, B gives a handkerchief to C, so C wins 2 supports and he is choosen to be the Hawk. ...

Summer Holiday (HDU - 1827) 题面 To see a World in a Grain of Sand And a Heaven in a Wild Flower, Hold Infinity in the palm of your hand And Eternity in an hour. —— William Blake 听说lcy帮大家预定了新马泰7日游，Wiskey真是高兴的夜不能寐啊，他想着得快点把这消息告诉大家，虽然他手上有所有人的联系方式，但是一个一个联系过去实在太耗时间和电话费了。他知道其他人也有一些别人的联系方式，这样他可以通知其他人，再让其他人帮忙通知一下别人。你能帮Wiskey计算出至少要通知多少人，至少得花多少电话费就能让所有人都被通知到吗？ ...

Proving Equivalences (HDU - 2767) 题面 Consider the following exercise, found in a generic linear algebra textbook. Let A be an n × n matrix. Prove that the following statements are equivalent: \1. A is invertible. \2. Ax = b has exactly one solution for every n × 1 matrix b. \3. Ax = b is consistent for every n × 1 matrix b. \4. Ax = 0 has only the trivial solution x = 0. ...

迷宫城堡 (HDU - 1269) 题面 为了训练小希的方向感，Gardon建立了一座大城堡，里面有N个房间(N<=10000)和M条通道(M<=100000)，每个通道都是单向的，就是说若称某通道连通了A房间和B房间，只说明可以通过这个通道由A房间到达B房间，但并不说明通过它可以由B房间到达A房间。Gardon需要请你写个程序确认一下是否任意两个房间都是相互连通的，即：对于任意的i和j，至少存在一条路径可以从房间i到房间j，也存在一条路径可以从房间j到房间i。 ...