BZOJ-1787Meet紧急集合 倍增LCA

Posted 2020-08-02 DaD3zZ

1787: [Ahoi2008]Meet 紧急集合

Time Limit: 20 Sec  Memory Limit: 162 MB
Submit: 2259  Solved: 1023
[Submit][Status][Discuss]

Description

Input

Output

Sample Input

6 4
1 2
2 3
2 4
4 5
5 6
4 5 6
6 3 1
2 4 4
6 6 6

Sample Output

5 2
2 5
4 1
6 0

HINT

Source

Day1

Solution

水题，随便倍增一下求LCA就可以

Code

#include<iostream>
#include<cstdio>
#include<cstring>
#include<algorithm>
#include<cmath>
using namespace std;
inline int read()
{
    int x=0,f=1; char ch=getchar();
    while (ch<‘0‘ || ch>‘9‘) {if (ch==‘-‘) f=-1; ch=getchar();}
    while (ch>=‘0‘ && ch<=‘9‘) {x=x*10+ch-‘0‘; ch=getchar();}
    return x*f;
}
#define maxn 500010
int n,m,deep[maxn],father[maxn][21];
struct EdgeNode{int next,to;}edge[maxn<<1];
int head[maxn],cnt;
void add(int u,int v) {cnt++; edge[cnt].next=head[u]; head[u]=cnt; edge[cnt].to=v;}
void insert(int u,int v) {add(u,v); add(v,u);}
void DFS(int now,int last)
{
    for (int i=1; i<=20; i++)
        if (deep[now]>=(1<<i)) father[now][i]=father[father[now][i-1]][i-1];
        else break;
    for (int i=head[now]; i; i=edge[i].next)
        if (edge[i].to!=last)
            {
                father[edge[i].to][0]=now;
                deep[edge[i].to]=deep[now]+1;
                DFS(edge[i].to,now);
            }
}
int LCA(int x,int y)
{
    if (deep[x]<deep[y]) swap(x,y);
    int dd=deep[x]-deep[y];
    for (int i=0; i<=20; i++)
        if ((1<<i)&dd) x=father[x][i];
    for (int i=20; i>=0; i--)
        if (father[x][i]!=father[y][i])
            x=father[x][i],y=father[y][i];
    if (x==y) return x; return father[x][0];
}
int Dist(int u,int v)
{
    int lca=LCA(u,v);
    return deep[u]+deep[v]-(deep[lca]<<1);
}
int ans,rt;
int main()
{
    n=read(); m=read();
    for (int u,v,i=1; i<=n-1; i++)
        u=read(),v=read(),insert(u,v);
    DFS(1,0);
    for (int x,y,z,i=1; i<=m; i++)
        {
            x=read(),y=read(),z=read();
            int fxy=LCA(x,y),fyz=LCA(y,z),fxz=LCA(x,z);
            rt=(fxy==fyz)? fxz : fxy==fxz? fyz : fxy;
            ans=Dist(x,rt)+Dist(y,rt)+Dist(z,rt);
            printf("%d %d\n",rt,ans);
        }
    return 0;
}

在学校被***毒的不能自拔，感觉已经不想在班里待下去了