2015-07-15 问题简述: 给出一组节点关系,判断由这些节点组成的图是否为一颗树. 树只有一个根节点,每个节点只有一条边指向它,没有环. 原题链接:http://poj.org/problem?id=1308 解题思路: 使用并查集判断是否只有一个根节点是很简单的——让并查集种祖先的父亲是他自己即可方便计算其数量,一旦祖先数量超过一,它就不是树: 也可使用并查集判断图是否有环——当两个即将要链接的节点都有相同的祖先时,这就产生了一个环. 源代码: /* OJ: HDOJ ID: forev…

POJ题目网址:http://poj.org/problem?id=1308 HDU题目网址:http://acm.hdu.edu.cn/showproblem.php?pid=1272 并查集的运用,如果想要形成一棵树,那么我们应该只能有一个根,并查集联合次数为节点数-1. //Asimple //#include <bits/stdc++.h> #include <iostream> #include <sstream> #include <algorithm…

Is It A Tree? Time Limit: 1000MS   Memory Limit: 10000K Total Submissions: 18778   Accepted: 6395 Description A tree is a well-known data structure that is either empty (null, void, nothing) or is a set of one or more nodes connected by directed edge…

DP/四边形不等式 这题跟石子合并有点像…… dp[i][j]为将第 i 个点开始的 j 个点合并的最小代价. 易知有 dp[i][j]=min{dp[i][j] , dp[i][k-i+1]+dp[k+1][j-(k-i+1)]+w(i,k,j)} (这个地方一开始写错了……) 即,将一棵树从k处断开成(i,k)和(k+1,i+j-1)两棵树,再加上将两棵树连起来的两条树枝的长度w(i,k,j) 其中,$ w(i,k,j)=x[k+1]-x[i]+y[k]-y[i+j-1] $ 那么根据四边形…

Is It A Tree? Time Limit: 2000/1000 MS (Java/Others)    Memory Limit: 65536/32768 K (Java/Others)Total Submission(s): 6961    Accepted Submission(s): 1619 [题目链接]http://acm.hdu.edu.cn/showproblem.php?pid=1325 这题如果用并查集做的话,最后判断的时候还是要看一个结点的入度是否为大于1(纯并查集的…

Is It A Tree? Time Limit: 1000MS   Memory Limit: 10000K Total Submissions: 24237   Accepted: 8311 Description A tree is a well-known data structure that is either empty (null, void, nothing) or is a set of one or more nodes connected by directed edge…

Is It A Tree? 题目链接: http://acm.hust.edu.cn/vjudge/contest/123393#problem/M Description A tree is a well-known data structure that is either empty (null, void, nothing) or is a set of one or more nodes connected by directed edges between nodes satisfy…

Is It A Tree? Time Limit: 1000MS   Memory Limit: 10000K Total Submissions: 31092   Accepted: 10549 Description A tree is a well-known data structure that is either empty (null, void, nothing) or is a set of one or more nodes connected by directed edg…

HDU认为1>2,3>2不是树,POJ认为是,而Virtual Judge上引用的是POJ数据这就是唯一的区别....(因为这个瞎折腾了半天) 此题因为是为了熟悉并查集而刷,其实想了下其实好好利用sort应该能更简单A掉,下次有空再去试试... 题目大意:判断是否为树,so: 1,无环: 2,除了根,所有的入度为1,根入度为0: 3,这个结构只有一个根,不然是森林了:4.空树也是树,即第一次输入的两个数字为0 0则是树,其他时候输入只是结束条件 因为POJ和HDU题面一样,要求不一样,所以这题…

Is It A Tree? Time Limit: 1000MS   Memory Limit: 10000K Total Submissions: 32052   Accepted: 10876 Description A tree is a well-known data structure that is either empty (null, void, nothing) or is a set of one or more nodes connected by directed edg…