题目
思路
显然先来一个最大生成树，然后我们用LCA求路径最小值即可。
code:
#include<iostream>
#include<cstdio>
#include<algorithm>
#include<string>
#include<cstring>
#include<cmath>
using namespace std;
long long fa[100010][22],v[100010][22],head[500010],c[500010],x,y,f[100010];
long long n,m,s;
struct f{
long long to,net,w;
} a[600020];
struct PVZ{
long long x,y,z;
bool o;
} z[300010];
long long k;
bool cmp(PVZ x,PVZ y)
{
return x.z>y.z;
}
long long find(long long x)
{
if (f[x]==x) return x;
else return f[x]=find(f[x]);
}
void add(long long u,long long v,long long z)
{
a[k].to=v;
a[k].w=z;
a[k].net=head[u];
head[u]=k++;
return;
}
void dk()
{
for (long long j=1;j<=m;j++)
{
if (find(z[j].x)!=find(z[j].y))
{
f[find(z[j].x)]=find(z[j].y);
add(z[j].x,z[j].y,z[j].z);
add(z[j].y,z[j].x,z[j].z);
}
}
return;
}
void dfs(long long x,long long f,long long g)
{
fa[x][0]=f;
v[x][0]=g;
c[x]=c[f]+1;
for (long long j=1;(1<<j)<=c[x];j++)
{
fa[x][j]=fa[fa[x][j-1]][j-1];
v[x][j]=min(v[x][j-1],v[fa[x][j-1]][j-1]);
}
for (long long i=head[x];i!=-1;i=a[i].net)
{
if (a[i].to!=f) dfs(a[i].to,x,a[i].w);
}
return;
}
long long mn=2147483647000000;
long long LCA(long long x,long long y)
{
if (find(x)!=find(y)) return -1;
if (c[x]>c[y]) swap(x,y);
long long mx1=0x7fffffff;
for (long long i=20;i>=0;i--)
{
if (c[x]<=c[y]-(1<<i))
{
mx1=min(mx1,v[y][i]);
y=fa[y][i];
}
}
if (x!=y)
{
for (long long i=20;i>=0;i--)
{
if (fa[x][i]==fa[y][i]) continue;
else
{
mx1=min(mx1,v[y][i]);
mx1=min(mx1,v[x][i]);
x=fa[x][i],y=fa[y][i];
}
}
mx1=min(mx1,v[x][0]);
mx1=min(mx1,v[y][0]);
x=fa[x][0];
y=fa[y][0];
}
return mx1;
}
int main()
{
memset(head,-1,sizeof(head));
cin>>n>>m;
for (long long i=1;i<=n;i++) f[i]=i;
for (long long i=1;i<=m;i++)
{
cin>>z[i].x>>z[i].y>>z[i].z;
if (z[i].x==z[i].y)
{
i--,m--;
}
}
sort(z+1,z+1+m,cmp);
dk();
dfs(1,0,0);
cin>>m;
for (long long i=1;i<=m;i++)
{
int x,y;
cin>>x>>y;
cout<<LCA(x,y)<<endl;
}
return 0;
}