#include<cstdio>
#include<iostream>
#include<cstring>
#define maxa 10000
using namespace std;
int f[maxa];
int fid(int x)
{
return f[x]==x?x:fid(f[x]);
}
void merge1(int x,int y)
{
int tt1 = fid(x);
int t2 =fid(y);
if(tt1!=t2)
{
f[tt1] =t2;
}
}
int main()
{
int n,m,p,i,x,y;
cin>>n>>m>>p;
for(i=1;i<=n;++i)
f[i] = i;
for(i=1;i<=m;++i)
{
cin>>x>>y;
merge1(x,y);
}
while(p--)
{
cin>>x>>y;
if(fid(x)==fid(y))
cout<<"Yes"<<endl;
else
cout<<"No"<<endl;
}
return 0;
}

论定义rank数组对1A的影响orzzz

#include<iostream>
using namespace std;
int n,m,p;
int par[5005],ran[5005];

void init(int q){
for(int i=1;i<=q;i++){
par[i]=i;
ran[i]=0;
}
}

int find(int x){
if(par[x]==x) return x;
else return par[x]=find(par[x]);
}

void unite(int a,int b){
a=find(a);
b=find(b);
if(a==b) return;
if(ran[a]<ran[b]) par[a]=b;
else{
par[b]=a;
if(ran[a]==ran[b]) ran[a]++;
}
}

bool same(int x,int y){
return find(x)==find(y);
}

int main(){
cin>>n>>m>>p;
init(n);
int res1,res2;
for(int i=1;i<=m;i++){
cin>>res1>>res2;
unite(res1,res2);
}
for(int i=1;i<=p;i++){
cin>>res1>>res2;
if(same(res1,res2)==true) cout<<"Yes"<<endl;
else cout<<"No"<<endl;
}
return 0;
}

裸的并查集，瑟瑟发抖
program exx(input,output);
var
n,m,p,i,x,y:longint;
fa:array[1..5000] of longint;
function gf(x:longint):longint;
begin
if fa[x]=x then exit(x);
fa[x]:=gf(fa[x]);
exit(fa[x]);
end;

procedure union(x,y:longint);
var
xx,yy:longint;
begin
xx:=gf(x);
yy:=gf(y);
fa[xx]:=yy;
end;
function ask(x,y:longint):boolean;
begin
if gf(x)=gf(y) then exit(true) else exit(false);
end;
begin
readln(n,m,p);
for i:=1 to n do
fa[i]:=i;
for i:=1 to m do
begin
readln(X,y);
union(x,y);
end;
for i:=1 to p do
begin
readln(x,y);
if ask(x,y) then writeln('Yes') else writeln('No');
end;
end.