3732: Network

来源：互联网发布：淘宝袜子好评语50字编辑：程序博客网时间：2024/06/06 09:54

题目链接

题目大意：同noip货车运输

题解：生成树+倍增

我的收获：水题++

#include <iostream>#include <cstdio>#include <queue>#include <cstring>#include <algorithm>using namespace std;const int M=15005;#define INF 0x3f3f3f3fint n,m,q,t;int f[M][21],l[M][21];int dis[M],dep[M];int fa[M],vis[M],head[M];struct edge{int to,vl,nex;}e[M*2];//存生成树图struct node{int u,v,vl;}a[M*2];//存初始图void add(int i,int j,int w){e[t].to=j,e[t].vl=w;e[t].nex=head[i];head[i]=t++;}bool cmp(node x,node y){return x.vl<y.vl;}void dfs(int x){    vis[x]=1;    for(int i=head[x];i!=-1;i=e[i].nex)    {        int v=e[i].to;        if(!vis[v]){            f[v][0]=x;            l[v][0]=e[i].vl;            dep[v]=dep[x]+1;            dfs(v);        }    }}int lca(int x,int y){    int mx=-INF;    if(dep[x]<dep[y]) swap(x,y);    for(int i=0;i<20;i++)if((dep[x]-dep[y])&(1<<i)) mx=max(mx,l[x][i]),x=f[x][i];    if(x==y)return mx;    for(int i=19;i>=0;i--)if(f[x][i]!=f[y][i]) mx=max(mx,max(l[x][i],l[y][i])),x=f[x][i],y=f[y][i];    return max(mx,max(l[x][0],l[y][0]));}int fid(int x){    return fa[x]==x?x:fa[x]=fid(fa[x]);}void uniom(int x,int y,int v){    int p=fid(x),q=fid(y);    if(p!=q) fa[p]=q,add(x,y,v),add(y,x,v);}void kruskal(){    for(int i=1;i<=n;i++) fa[i]=i;    for(int i=1;i<=m;i++)    uniom(a[i].u,a[i].v,a[i].vl);}void cl(){    for(int j=1;j<=20;j++)        for(int i=1;i<=n;i++)            f[i][j]=f[f[i][j-1]][j-1],            l[i][j]=max(l[i][j-1],l[f[i][j-1]][j-1]);}void work(){    kruskal();    for(int i=1;i<=n;i++)     if(!vis[i]) dfs(i);    cl();    int x,y;    for(int i=1;i<=q;i++)        scanf("%d%d",&x,&y),printf("%d\n",lca(x,y));}void init(){    memset(head,-1,sizeof(head));    scanf("%d%d%d",&n,&m,&q);    for(int i=1;i<=m;i++)        scanf("%d%d%d",&a[i].u,&a[i].v,&a[i].vl);    sort(a+1,a+1+m,cmp);}int main(){    init();    work();    return 0;}

0 0