题意: 有n个点,m条边,其中有单向边和双向边,求是否存在欧拉回路 解析: 刚开始想...判断一下每个点的度数不就好了...emm..还是年轻啊.. 判断是解决不了问题的,因为可能会有某两个点冲突,比如说一个点出度比入度大1,但它只有一条无向边,所以这条无向边要变成入边,但这条无向边的v点也是 出度比入度大1,也是需要一条入边,所以这样就会冲突,如果直接判断的话不会判断出来,所以就用到了网络流, 设想一下,我们把这条无向边的容量设为1,那么如果用了这条边,容量就会为0,所以不会重复使用,且不产生…

描述 The city executive board in Lund wants to construct a sightseeing tour by bus in Lund, so that tourists can see every corner of the beautiful city. They want to construct the tour so that every street in the city is visited exactly once. The bus s…

题目链接:http://acm.hdu.edu.cn/showproblem.php?pid=1956 思路:先将无向边定向,比如1<->3,可以定它的方向为1->3,1的出度++,3的入度++即可.读入的时候如果遇到无向边,把这条边加入待建的网络中,流量为1.读入完后,然后用出度减入度得到x,如果x为奇数,肯定不存在欧拉回路,如果没有奇数,就用最大流求解. 如果x大于0,则建一条s(源点)到当前点容量为x/2的边,如果x小于0,建一条从当前点到 t(汇点)容量为|x/2|的边.然后求最…

有向连通图存在欧拉回路的充要条件是所有点入度=出度. 首先随便给定所有无向边一个方向(不妨直接是u->v方向),记录所有点的度(记:度=入度-出度). 这时如果有点的度不等于0,那么就不存在欧拉回路,就需要改变那些无向边的方向. 而改变一个无向边的方向,相当于边上两个端点的入度和出度都变化了1,它们的度±2. 另外,这样可以证明如果这时某个点的度为奇数那么一定不存在存在欧拉回路的解. 构图如下:所有无向边(u,v),建立容量为1的(u,v)边:所有度小于0的点u,建立容量为-deg/2的(vs,…

                                                            Sightseeing tour Time Limit: 1000MS   Memory Limit: 10000K Total Submissions: 9100   Accepted: 3830 Description The city executive board in Lund wants to construct a sightseeing tour by bus…

嗯,这是我上一篇文章说的那本宝典的第二题,我只想说,真TM是本宝典……做的我又痛苦又激动……(我感觉ACM的日常尽在这张表情中了) 题目链接:http://poj.org/problem?id=1637 Time Limit: 1000MS Memory Limit: 10000K Description The city executive board in Lund wants to construct a sightseeing tour by bus in Lund, so that t…

题目链接:http://poj.org/problem?id=1637 Sightseeing tour Time Limit: 1000MS   Memory Limit: 10000K Total Submissions:10837   Accepted: 4560 Description The city executive board in Lund wants to construct a sightseeing tour by bus in Lund, so that tourist…

Sightseeing tour Time Limit: 1000MS   Memory Limit: 10000K Total Submissions: 10581   Accepted: 4466 题目链接:http://poj.org/problem?id=1637 Description: The city executive board in Lund wants to construct a sightseeing tour by bus in Lund, so that touri…

Sightseeing tour   Description The city executive board in Lund wants to construct a sightseeing tour by bus in Lund, so that tourists can see every corner of the beautiful city. They want to construct the tour so that every street in the city is vis…

Sightseeing tour Time Limit: 1000MS   Memory Limit: 10000K Total Submissions: 6986   Accepted: 2901 Description The city executive board in Lund wants to construct a sightseeing tour by bus in Lund, so that tourists can see every corner of the beauti…