HDU 4871 Shortest-path tree (最短路+树上点分治)

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题目地址：HDU 4871
先用最短路求出根节点到其它各点的最短距离，然后利用最短距离DFS一下构造出最短路树，然后剩下的就是在构造出来的这棵树上做树分治，很简单的树分治。
代码如下：
#include <iostream>#include <string.h>#include <math.h>#include <queue>#include <algorithm>#include <stdlib.h>#include <map>#include <set>#include <stdio.h>#include <time.h>using namespace std;#define LL __int64#define pi acos(-1.0)#pragma comment(linker, "/STACK:1024000000")const int mod=1e6+3;const int INF=0x3f3f3f3f;const double eqs=1e-9;const int MAXN=30000+10;vector<pair<int,int> >G[MAXN];int head[MAXN], cnt, root, k, min1, ff, ansdep, Maxdep;LL ansnum;int d[MAXN], vis[MAXN], siz[MAXN];int dep[MAXN], flag[MAXN], Max[MAXN];LL dp[MAXN], Maxcnt[MAXN];struct node{        int v, w, next;}edge[MAXN<<1];void add(int u, int v, int w){        edge[cnt].v=v;        edge[cnt].w=w;        edge[cnt].next=head[u];        head[u]=cnt++;}void spfa(){        queue<int>q;        q.push(1);        memset(vis,0,sizeof(vis));        memset(d,INF,sizeof(d));        d[1]=0;        vis[1]=1;        while(!q.empty()){                int u=q.front();                q.pop();                vis[u]=0;                for(int i=0;i<G[u].size();i++){                        int v=G[u][i].first;                        if(d[v]>d[u]+G[u][i].second){                                d[v]=d[u]+G[u][i].second;                                if(!vis[v]){                                        vis[v]=1;                                        q.push(v);                                }                        }                }        }}void dfs(int u){        vis[u]=1;        for(int i=0;i<G[u].size();i++){                int v=G[u][i].first;                if(vis[v]) continue ;                if(d[v]==d[u]+G[u][i].second){                        add(u,v,G[u][i].second);                        add(v,u,G[u][i].second);                        //printf("%d %d\n",u,v);                        dfs(v);                }        }}void build_tree(int n){        memset(vis,0,sizeof(vis));        for(int i=1;i<=n;i++){                sort(G[i].begin(),G[i].end());        }        dfs(1);}void init(int n){        for(int i=1;i<=n;i++){                G[i].clear();        }        memset(head,-1,sizeof(head));        cnt=0;}void getsize(int u, int fa){        siz[u]=1;        for(int i=head[u];i!=-1;i=edge[i].next){                int v=edge[i].v;                if(v==fa||vis[v]) continue ;                getsize(v,u);                siz[u]+=siz[v];        }}void getroot(int u, int fa, int s){        int max1=0;        for(int i=head[u];i!=-1;i=edge[i].next){                int v=edge[i].v;                if(v==fa||vis[v]) continue ;                getroot(v,u,s);                max1=max(max1,siz[v]);        }        max1=max(max1,s-siz[u]);        if(min1>max1){                min1=max1;                root=u;        }}void getMaxdep(int depp, int u, int fa){        Maxdep=max(Maxdep,depp);        for(int i=head[u];i!=-1;i=edge[i].next){                int v=edge[i].v;                if(v==fa||vis[v]) continue ;                getMaxdep(depp+1,v,u);        }}void getdep(int depp, int len, int u, int fa){        if(dep[depp]<len){                dep[depp]=len;                dp[depp]=1;        }        else if(dep[depp]==len) dp[depp]++;        if(depp>=k) return ;        for(int i=head[u];i!=-1;i=edge[i].next){                int v=edge[i].v;                if(v==fa||vis[v]) continue ;                getdep(depp+1,len+edge[i].w,v,u);        }}void work(int u){        vis[u]=1;        int i, j, tmp;        for(i=head[u];i!=-1;i=edge[i].next){                int v=edge[i].v;                if(vis[v]) continue ;                min1=INF;                getsize(v,-1);                getroot(v,-1,siz[v]);                work(root);        }        ff++;        flag[0]=ff;        dep[0]=0;        dp[0]=1;        Maxcnt[0]=1;        Max[0]=0;        for(i=head[u];i!=-1;i=edge[i].next){                int v=edge[i].v;                if(vis[v]) continue ;                Maxdep=-1;                getMaxdep(1,v,u);                for(j=0;j<=Maxdep&&j<=k;j++) dep[j]=-1;                getdep(1,edge[i].w,v,u);                for(j=0;j<=Maxdep&&j<k;j++){                        tmp=k-j-1;                        if(flag[tmp]!=ff) continue ;                        if(ansdep<Max[tmp]+dep[j]){                                ansdep=Max[tmp]+dep[j];                                ansnum=Maxcnt[tmp]*dp[j];                        }                        else if(ansdep==Max[tmp]+dep[j]){                                ansnum+=Maxcnt[tmp]*dp[j];                        }                }                for(j=1;j<=Maxdep&&j<k;j++){                        if(flag[j]!=ff||Max[j]<dep[j]){                                Max[j]=dep[j];                                Maxcnt[j]=dp[j];                                flag[j]=ff;                        }                        else if(flag[j]==ff&&Max[j]==dep[j]){                                Maxcnt[j]+=dp[j];                        }                }        }        vis[u]=0;}int main(){        int t, n, m, i, u, v, w;        scanf("%d",&t);        while(t--){                scanf("%d%d%d",&n,&m,&k);                init(n);                while(m--){                        scanf("%d%d%d",&u,&v,&w);                        G[u].push_back(make_pair(v,w));                        G[v].push_back(make_pair(u,w));                }                spfa();                build_tree(n);                memset(vis,0,sizeof(vis));                memset(flag,-1,sizeof(flag));                ff=0;                ansdep=0;                min1=INF;                getsize(1,-1);                getroot(1,-1,n);                work(root);                printf("%d %I64d\n",ansdep,ansnum);        }        return 0;}
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