UVa:1267 Network

来源：互联网发布：2015网络作家收入编辑：程序博客网时间：2024/05/16 04:54

自己胡乱想的思路居然AC了，真是泪流满脸啊。。

首先要无根树化为有根树，这个刘汝佳第一本书上有。然后dfs取所有叶结点，并按照其深度从大到小排序。这样依次判断每个叶结点，首先对于该叶结点访问与它距离k以内的所有结点看是否为服务器，如果没有则要从该叶结点往上沿着父亲结点遍历，选距离k的那个结点放置服务器。

#include <iostream>#include <cstdio>#include <cstring>#include <string>#include <cmath>#include <vector>#include <queue>#include <map>#include <algorithm>#define ll long long#define INF 2139062143#define inf -2139062144#define MOD 20071027#define MAXN 1005using namespace std;struct Tree{    int father;    vector<int> child;};struct Node{    int num,deep;};vector<Node> vec;int n,k,s;Tree tree[MAXN];bool flag[MAXN],vis[MAXN];bool gl[MAXN][MAXN],leave[MAXN];int ans;void Init(){    for(int i=0; i<=n; ++i)    {        tree[i].child.clear();        tree[i].father=0;    }    vec.clear();    memset(gl,0,sizeof(gl));    memset(leave,0,sizeof(leave));}void getnode(int u,int d){    if(tree[u].child.size()==0)    {        vec.push_back(Node {u,d});        leave[u]=true;    }    else    {        for(int i=0; i<tree[u].child.size(); ++i)            getnode(tree[u].child[i],d+1);    }}bool search(int u,int d){    if(d<=k)    {        vis[u]=true;        if(flag[u]) return true;        for(int i=0; i<tree[u].child.size(); ++i)            if(!vis[tree[u].child[i]]&&search(tree[u].child[i],d+1)) return true;        if(!vis[tree[u].father]&&search(tree[u].father,d+1)) return true;        return false;    }    return false;}bool makeflag(int u,int d){    if(d<=k)    {        if(d==k)        {            flag[u]=true;            return true;        }        if(makeflag(tree[u].father,d+1)) return true;        return false;    }    return false;}bool cmp(Node a,Node b){    return a.deep>b.deep;}void maketree(int u,int f){    tree[u].father=f;    for(int i=1; i<=n; ++i)        if(gl[u][i]&&i!=f)        {            tree[u].child.push_back(i);            maketree(i,u);        }}int main(){    int T;    //freopen("asdf.txt","w",stdout);    scanf("%d",&T);    while(T--)    {        scanf("%d",&n);        scanf("%d%d",&s,&k);        Init();        for(int i=1; i<n; ++i)        {            int x,y;            scanf("%d%d",&x,&y);            gl[x][y]=gl[y][x]=true;        }        maketree(s,-1);        ans=0;        getnode(s,0);        sort(vec.begin(),vec.end(),cmp);        memset(flag,0,sizeof(flag));        flag[s]=true;        for(int i=0; i<vec.size(); ++i)        {            memset(vis,0,sizeof(vis));            if(!search(vec[i].num,0))            {                makeflag(vec[i].num,0);                ans++;            }        }        printf("%d\n",ans);    }    return 0;}

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