传送门 分析 见ptx大爷的博客 代码 #include<iostream> #include<cstdio> #include<cstring> #include<string> #include<algorithm> #include<cctype> #include<cmath> #include<cstdlib> #include<queue> #include<ctime> #…

题目大意: 给你一棵树,边权都是1,每一个点有一个是起点的概率和一个是终点的概率,你将以起点为根,开始在树上随机dfs,每到一个点,就会将他的所有儿子随机打乱成序列,然后按照那个随机顺序走完,直到走到终点.求dfs从起点到终点的期望长度. 其实一开始看到这个题,还是有点懵逼的啊 根据期望的线性性,我们可以通过求所有相邻点的期望,然后直接相加,得到ans 那我们可以这么考虑,对于一个点来说,假设我们要求的是从\(x->y\)(\(y\)是\(x\)的儿子)的期望的话,如果走到一个错的儿子,那么就需…

Portal --> cf123E Solution 首先步数的话可以转化成每条边经过了几次这样来算 假设现在确定了起点\(S\)和终点\(T\),我们将\(T\)看成树根,那么考虑边\((u,v)\)的经过次数可以分成下面三种情况: 1.\((u,v)\)在\(S\)到\(T\)的路径上,那么这条边肯定要被经过,期望为1 2.\((u,v)\)不在\(S\)到\(T\)的路径上,但是在\(T\)包含\(S\)的那个儿子的子树里面,那么这条边有两种情况:被经过\(2\)次或者不被经过 考虑一下经…

Sept. 10, 2015 Study again the back tracking algorithm using recursive solution, rat in maze, a classical problem. Made a few of mistakes through the practice, one is how to use two dimension array, another one is that "not all return path returns va…

http://www.lightoj.com/volume_showproblem.php?problem=1027 You are in a maze; seeing n doors in front of you in beginning. You can choose any door you like. The probability for choosing a door is equal for all doors. If you choose the ith door, it ca…

1204.   Maze Traversal A common problem in artificial intelligence is negotiation of a maze. A maze has corridors and walls. The robot can proceed along corridors, but cannot go through walls. Input For this problem, you will input the dimensions of…

/*这道题我原本是将斜线迷宫扩大为原来的两倍,但是在这种情况下对于在斜的方向上的搜索会变的较容易出错,所以参考了别人的思路后将迷宫扩展为原来的3倍,这样就变成一般的迷宫问题了*/ #include"iostream" #include"stdio.h" #include"algorithm" #include"cmath" #include"string.h" #include"ctype.h&q…

Zhuge Liang's Stone Sentinel Maze Time Limit: 10000/4000 MS (Java/Others)    Memory Limit: 32768/32768 K (Java/Others)Total Submission(s): 385    Accepted Submission(s): 106 Problem Description Zhuge Liang was a chancellor of the state of Shu Han dur…

Borg Maze Time Limit: 1000MS   Memory Limit: 65536K Total Submissions: 9220   Accepted: 3087 Description The Borg is an immensely powerful race of enhanced humanoids from the delta quadrant of the galaxy. The Borg collective is the term used to descr…

Time Limit: 1000MS   Memory Limit: 65536K Total Submissions: 9718   Accepted: 3263 Description The Borg is an immensely powerful race of enhanced humanoids from the delta quadrant of the galaxy. The Borg collective is the term used to describe the gr…