05-树8 File Transfer

We have a network of computers and a list of bi-directional connections. Each of these connections allows a file transfer from one computer to another. Is it possible to send a file from any computer on the network to any other?

Input Specification:

Each input file contains one test case. For each test case, the first line contains N (2≤N≤10​4​​), the total number of computers in a network. Each computer in the network is then represented by a positive integer between 1 and N. Then in the following lines, the input is given in the format:

I c1 c2

where I stands for inputting a connection between c1 and c2; or

C c1 c2

where C stands for checking if it is possible to transfer files between c1and c2; or

S

where S stands for stopping this case.

Output Specification:

For each C case, print in one line the word "yes" or "no" if it is possible or impossible to transfer files between c1 and c2, respectively. At the end of each case, print in one line "The network is connected." if there is a path between any pair of computers; or "There are k components." where kis the number of connected components in this network.

Sample Input 1:

5C 3 2I 3 2C 1 5I 4 5I 2 4C 3 5S

Sample Output 1:

nonoyesThere are 2 components.

Sample Input 2:

5C 3 2I 3 2C 1 5I 4 5I 2 4C 3 5I 1 3C 1 5S

Sample Output 2:

nonoyesyesThe network is connected.

思路：

这题用并查集做很简单，要知道为什么要用并查集

#include <iostream>#include <cstdio>using namespace std;int count;int Find(int x,int s[]){    if(s[x]<=0)        return x;    else return s[x] = Find(s[x], s);}void Union(int x1, int x2, int s[]){    int root1 = Find(x1, s);    int root2 = Find(x2, s);    if(root1!=root2)    {        if(s[root2] < s[root1])        {            s[root2]+=s[root1];            s[root1] = root2;            count--;        }        else        {            s[root1]+=s[root2];            s[root2] = root1;            count--;        }    }}void initiaSet(int s[],int n){    for(int i=1;i<n+1;i++)    {        s[i] = -1;    }}int main(){    int n;    cin>>n;    count = n;    int *s = new int[n];    initiaSet(s,n);    char ch;    cin>>ch;    while(ch!='S')    {        int x,y;        cin>>x>>y;        if(ch == 'C')        {            if(Find(x,s) == Find(y,s)) printf("yes\n");            else printf("no\n");        }        else if(ch == 'I')        {            Union(x, y, s);        }        cin>>ch;    }    if(count == 1) printf("The network is connected.\n");    else printf("There are %d components.\n",count);    return 0;}