BZOJ1787_紧急集合_KEY

题目传送门

LCA，对于每一个(x,y,z)，两两求LCA得最优解或求出LCA不同于其他两组的那个为最优解。

code：

/**************************************************************
    Problem: 1787
    User: yekehe
    Language: C++
    Result: Accepted
    Time:5212 ms
    Memory:51604 kb
****************************************************************/
 
#include <cstdio>
#include <cstring>
#include <algorithm>
using namespace std;
 
int read()
{
    char c;while(c=getchar(),c<'0'||c>'9');
    int x=c-'0';while(c=getchar(),c>='0'&&c<='9')x=(x<<1)+(x<<3)+c-'0';
    return x;
}
 
const int MAXN=500005;
int N,M;
int head[MAXN],to[MAXN<<1],nxt[MAXN<<1],cnt;
void add(int x,int y)
{
    to[cnt]=y;
    nxt[cnt]=head[x];
    head[x]=cnt;
    cnt++;
}
 
int D[MAXN];
int f[20][MAXN];
void dfs(int now,int deep,int fa)
{
    D[now]=deep;
    f[0][now]=fa;
        for(int i=head[now];i!=-1;i=nxt[i])
            if(!D[to[i]])
                dfs(to[i],deep+1,now);
    return ;
}
int Me;
int get(int x,int y)
{
    if(D[x]<D[y])swap(x,y);
    for(int i=19;i>=0;i--)
        if(D[f[i][x]]>=D[y])x=f[i][x];
    if(x==y)return x;
    for(int i=19;i>=0;i--)
        if(f[i][x]!=f[i][y])
            x=f[i][x],y=f[i][y];
    return f[0][x];
}
 
int solve(int x,int y)
{
    return D[x]+D[y]-(D[get(x,y)]<<1);
}
int main(){
    memset(head,-1,sizeof head);
    memset(nxt,-1,sizeof nxt);
    N=read(),M=read();
    register int i,j;
        for(i=1;i<N;i++){
            int x=read(),y=read();
            add(x,y),add(y,x);
        }
    dfs(1,1,0);
        for(i=1;i<=19;i++)
            for(j=1;j<=N;j++)
                f[i][j]=f[i-1][f[i-1][j]];
        for(i=1;i<=M;i++){
            int x=read(),y=read(),z=read();
            int a=get(x,y),b=get(y,z),c=get(x,z);
            int dist=0;
            if(a==b)dist=c;else
            if(b==c)dist=a;else
            dist=b;
            printf("%d %d\n",dist,solve(x,dist)+solve(y,dist)+solve(z,dist));
        }
    return 0;
}