hdu 4607

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树的直径
题目已经说明是不会出现环了
#include <cstdio>#include <iostream>#include <cstring>#include <vector>#include <queue>using namespace std;int const MAXN = 100010;typedef struct EDGE{    int to;    int w;}Edge;vector <Edge> edge[MAXN];int vis[MAXN],dis[MAXN];int n,m;void Init(){    for(int i = 0;i < MAXN;i++){        edge[i].clear();    }}void Add(int u,int v){    Edge temp;    temp.w = 1;    temp.to = v;    edge[u].push_back(temp);    temp.to = u;    edge[v].push_back(temp);}void Bfs(int start){    memset(dis,0,sizeof(dis));    memset(vis,0,sizeof(vis));    vis[start] = 1;    dis[start] = 0;    queue <int> q;    while(!q.empty()){        q.pop();    }    q.push(start);    while(!q.empty()){        int top = q.front();        q.pop();        for(int i = 0;i < edge[top].size();i++){            int to = edge[top][i].to;            if(!vis[to]){                vis[to] = 1;                dis[to] = dis[top] + edge[top][i].w;                q.push(to);            }        }    }}int Count(int start){    int u = start,maxx = 0;    Bfs(u);    for(int i = 1;i <= n;i++){        if(dis[i] > maxx){            u = i;            maxx = dis[i];        }    }    Bfs(u);    maxx = 0;    for(int i = 1;i <= n;i++){        if(dis[i] > maxx) maxx = dis[i];    }    return maxx;}int main(){    int T,x;    while(~scanf("%d",&T)){        while(T--){            Init();            scanf("%d%d",&n,&m);            for(int i = 0;i < n - 1;i++){                int u,v;                scanf("%d%d",&u,&v);                Add(u,v);                x = u;            }            int maxx;            maxx = Count(x);            while(m--){                scanf("%d",&x);                if(x - 1 <= maxx) printf("%d\n",x - 1);                else printf("%d\n",2 * (x - maxx - 1) + maxx);            }        }    }    return 0;}
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