122 lines
2.2 KiB
C++
122 lines
2.2 KiB
C++
#include<cstdio>
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#include<cstring>
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#include<vector>
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#include<algorithm>
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using namespace std;
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const int maxn=10005;
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const int maxm=50005;
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const int oo=0x3f3f3f3f;
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struct Edge { int v,w; Edge *next; };
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Edge mem[maxm*2],*G[maxn],*ecnt=mem;
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inline void AddEdge(int u,int v,int w) { ecnt->v=v; ecnt->w=w; ecnt->next=G[u]; G[u]=ecnt++; }
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int n,m,q;
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namespace LinkSet
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{
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int fa[maxn];
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void init() { for(int i=1;i<=n;i++) fa[i]=i; }
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int ff(int x)
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{
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int a=x,b;
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while(x!=fa[x]) x=fa[x];
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while(a!=x)
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{
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b=fa[a];
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fa[a]=x;
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a=b;
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}
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return x;
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}
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}
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namespace Kruskal
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{
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struct EDGE { int u,v,w; };
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inline bool operator<(const EDGE &a,const EDGE &b) { return a.w>b.w; }
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vector<EDGE> e;
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inline void AddEdge(int u,int v,int w) { e.push_back((EDGE){u,v,w}); }
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void kruskal()
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{
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using namespace LinkSet;
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sort(e.begin(),e.end());
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int cnt=0,es=e.size();
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for(int i=0;i<es&&cnt<n-1;i++)
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{
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int x=e[i].u,y=e[i].v,fx=ff(x),fy=ff(y);
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if(fx==fy) continue;
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fa[fx]=fy; cnt++;
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::AddEdge(x,y,e[i].w); ::AddEdge(y,x,e[i].w);
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}
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}
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}
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bool vis[maxn];
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int f[maxn][21],w[maxn][21],deep[maxn];
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void dfs(int u,int fa)
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{
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vis[u]=true;
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for(Edge *it=G[u];it;it=it->next)
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{
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int v=it->v;
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if(v==fa) continue;
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f[v][0]=u;
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w[v][0]=it->w;
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deep[v]=deep[u]+1;
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dfs(v,u);
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}
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}
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int GetLCA(int x,int y)
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{
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using namespace LinkSet;
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if(ff(x)!=ff(y)) return -1;
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int res=oo;
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if(deep[x]<deep[y]) swap(x,y);
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for(int i=20;i>=0;i--)
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if(deep[f[x][i]]>=deep[y])
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{
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res=min(res,w[x][i]);
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x=f[x][i];
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}
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if(x==y) return res;
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for(int i=20;i>=0;i--)
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if(f[x][i]!=f[y][i])
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{
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res=min(res,min(w[x][i],w[y][i]));
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x=f[x][i];
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y=f[y][i];
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}
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res=min(res,min(w[x][0],w[y][0]));
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return res;
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}
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int main()
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{
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#ifdef local
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freopen("pro.in","r",stdin);
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#endif
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scanf("%d%d",&n,&m);
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while(m-->0)
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{
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int x,y,z; scanf("%d%d%d",&x,&y,&z);
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Kruskal::AddEdge(x,y,z);
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}
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LinkSet::init();
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Kruskal::kruskal();
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memset(w,0x3f,sizeof(w));
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for(int i=1;i<=n;i++)
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if(!vis[i])
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{
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deep[i]=1;
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dfs(i,-1);
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}
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for(int i=1;i<=20;i++)
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for(int j=1;j<=n;j++)
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{
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f[j][i]=f[f[j][i-1]][i-1];
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w[j][i]=min(w[j][i-1],w[f[j][i-1]][i-1]);
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}
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scanf("%d",&q);
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while(q-->0)
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{
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int x,y; scanf("%d%d",&x,&y);
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printf("%d\n",GetLCA(x,y));
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}
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return 0;
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}
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