做完bzoj2959，再做这道题就显得比较简单了。我们要维护一个边双联通分量大小。用并查集来缩点即可。
#include <cstdio> #include <cstring> #include <algorithm> #include <queue> using namespace std; #define ll long long #define inf 0x3f3f3f3f #define N 200010 inline int read(){ int x=0,f=1;char ch=getchar(); while(ch<'0'||ch>'9'){if(ch=='-')f=-1;ch=getchar();} while(ch>='0'&&ch<='9') x=x*10+ch-'0',ch=getchar(); return x*f; } int n,m,mm,fa[N],c[N][2],sz[N],v[N],fa1[N],fa2[N],q[N]; bool rev[N]; inline int find1(int x){ return x==fa1[x]?x:fa1[x]=find1(fa1[x]); } inline int find2(int x){ return x==fa2[x]?x:fa2[x]=find2(fa2[x]); } inline void dfs(int x,int rt){ fa2[x]=rt; if(c[x][0]) dfs(c[x][0],rt); if(c[x][1]) dfs(c[x][1],rt); } inline bool isroot(int x){ return x!=c[find2(fa[x])][0]&&x!=c[find2(fa[x])][1]; } inline void update(int x){ int l=c[x][0],r=c[x][1]; sz[x]=sz[l]+sz[r]+v[x]; } inline void pushdown(int x){ if(!rev[x]) return;rev[x]=0;int l=c[x][0],r=c[x][1]; rev[l]^=1;rev[r]^=1;swap(c[x][0],c[x][1]); } inline void rotate(int x){ int y=find2(fa[x]),z=find2(fa[y]),l=x==c[y][1],r=l^1; if(!isroot(y)) c[z][y==c[z][1]]=x; fa[c[x][r]]=y;fa[y]=x;fa[x]=z; c[y][l]=c[x][r];c[x][r]=y;update(y);update(x); } inline void splay(int x){ int top=0;q[++top]=x; for(int xx=x;!isroot(xx);xx=find2(fa[xx])) q[++top]=find2(fa[xx]); while(top) pushdown(q[top--]); while(!isroot(x)){ int y=find2(fa[x]),z=find2(fa[y]); if(!isroot(y)){ if(x==c[y][1]^y==c[z][1]) rotate(x); else rotate(y); }rotate(x); } } inline void access(int x){ int y=0; while(x) splay(x),c[x][1]=y,update(x),y=x,x=find2(fa[x]); } inline void makeroot(int x){ access(x);splay(x);rev[x]^=1; } inline void link(int x,int y){ makeroot(x);fa[x]=y; } int main(){ // freopen("a.in","r",stdin); n=read();mm=read();m=read(); for(int i=1;i<=n;++i) fa1[i]=fa2[i]=i,v[i]=1; while(mm--){ int x=read(),y=read(); x=find2(x);y=find2(y); int xx=find1(x),yy=find1(y); if(xx!=yy){fa1[xx]=yy,link(x,y);continue;} if(x==y) continue; makeroot(x);access(y);splay(y);v[y]=sz[y];dfs(y,y); }while(m--){ int x=read(),y=read(); x=find2(x);y=find2(y); int xx=find1(x),yy=find1(y); if(xx!=yy){fa1[xx]=yy,link(x,y);puts("No");continue;} if(x==y){printf("%d\n",v[x]);continue;} makeroot(x);access(y);splay(y);v[y]=sz[y];dfs(y,y); printf("%d\n",v[y]);continue; }return 0; }