1752. Tree 2 （数据结构）

找出树直径的两个端点，找出所有点到这两个点的距离。

对每一个询问。查看被询问点到两个端点距离为k的点，如果存在就输出。

#include <iostream>#include <cmath>#include <cstdio>#include <cstring>#include <algorithm>#include <queue>#include <stack>#include <map>#include <set>#include <list>#include <deque>#include <string>#define LL long long#define DB double#define SI(a) scanf("%d",&a)#define SD(a) scanf("%lf",&a)#define SS(a) scanf("%s",a)#define SF scanf#define PF printf#define MM(a,v) memset(a,v,sizeof(a))#define REP(i,a,b) for(int (i)=(a);(i)<(b);(i)++)#define REPD(i,a,b) for(int (i)=(a);(i)>(b);(i)--)#define N 20009#define INF 0x3f3f3f3f#define EPS 1e-8#define bug puts("bug")using namespace std;int dp1[N][16],dp2[N][16];vector<int> L[N];int n,q;queue<int> que;int dis[N];int visit[N];int fin(int k){    MM(dis,INF);    int ret;    que.push(k);    dis[k] = 0;    while(!que.empty())    {        int e = que.front();que.pop();        ret = e;        REP(i,0,(int)L[e].size())        {            int to = L[e][i];            if(dis[to]==INF)            {                dis[to] = dis[e]+1;                que.push(to);            }        }    }return ret;}void dfs(int k,int dp[][16]){    REP(i,0,(int)L[k].size())    {        int to = L[k][i];        if(visit[to]) continue;        visit[to] = 1;        dp[to][0] = k;        REP(j,1,16)        {            dp[to][j] = dp[dp[to][j-1]][j-1];            if(dp[to][j]==0) break;        }        dfs(to,dp);    }}void ini(){    int rt1 = fin(1);    int rt2 = fin(rt1);    MM(visit,0);    visit[rt1] = 1;    dfs(rt1,dp1);    MM(visit,0);    visit[rt2] = 1;    dfs(rt2,dp2);}int solve(int k,int d){    if(d==0) return k;    int ret = k;    REPD(i,30,-1)    {        if(d&(1<<i))        ret = dp1[ret][i];        if(ret==0) break;    }    if(ret) return ret;    ret = k;    REPD(i,30,-1)    {        if(d&(1<<i))        ret = dp2[ret][i];        if(ret==0) break;    }    return ret;}int main(){    #ifndef ONLINE_JUDGE    freopen("in.txt","r",stdin);    #endif    SI(n);SI(q);    int a,b;    REP(i,1,n)    {        SI(a);SI(b);        L[a].push_back(b);        L[b].push_back(a);    }    ini();    while(q--)    {        SI(a);SI(b);        PF("%d\n",solve(a,b));    }    return 0;}