7-1 File Transfer(25 分)
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≤104), 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 c1
and 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 k
is the number of connected components in this network.
Sample Input 1:
5
C 3 2
I 3 2
C 1 5
I 4 5
I 2 4
C 3 5
S
Sample Output 1:
no
no
yes
There are 2 components.
Sample Input 2:
5
C 3 2
I 3 2
C 1 5
I 4 5
I 2 4
C 3 5
I 1 3
C 1 5
S
Sample Output 2:
no
no
yes
yes
The network is connected.
思路:很明显的并查集
代码如下:
#include<iostream>
#include<set>
using namespace std;
int k[10005];
char p;
int find(int x){
int a=x;
while(k[x]!=x) x=k[x];
while(a!=k[a]){
int z=a;
a=k[a];
k[z]=x;
}
return x;
}
void union1(int a,int b){
int fa=find(a);
int fb=find(b);
if(fa!=fb) k[fa]=fb;
}
int main()
{
set<int>st;
int n,a,b;
scanf("%d",&n);
for(int i=1;i<=n;i++) k[i]=i;
while(cin>>p,p!='S'){
cin>>a>>b;
if(p=='I'){
union1(a,b);
}
else{
if(k[find(a)]!=k[find(b)]) cout<<"no"<<endl;
else cout<<"yes"<<endl;
}
}
for(int i=1;i<=n;i++){
//cout<<i<<k[find(i)]<<endl;
st.insert(k[find(i)]);
}
if(st.size()==1) cout<<"The network is connected."<<endl;
else cout<<"There are "<<st.size()<<" "<<"components."<<endl;
}