[AHOI 2008] 聚会

[题目链接]

          https://www.lydsy.com/JudgeOnline/problem.php?id=1832

[算法]

          最近公共祖先

[代码]

         

#include<bits/stdc++.h>
using namespace std;
#define MAXN 500010
#define MAXLOG 20

struct edge
{
        int to,nxt;
} e[MAXN << 1];
int i,n,m,u,v,a,b,c,tot,l1,l2,l3,t;
int head[MAXN],depth[MAXN];
int anc[MAXN][MAXLOG];

inline void addedge(int u,int v)
{
        tot++;
        e[tot] = (edge){v,head[u]};
        head[u] = tot;
}
inline void dfs(int u)
{
        int i,v;
        for (i = 1; i < MAXLOG; i++)
        {
                if (depth[u] < (1 << i)) continue;
                anc[u][i] = anc[anc[u][i - 1]][i - 1];
        }
        for (i = head[u]; i; i = e[i].nxt)
        {
                v = e[i].to;
                if (v != anc[u][0]) 
                {
                        depth[v] = depth[u] + 1;
                        anc[v][0] = u;
                        dfs(v);
                }
        }
}
inline int lca(int u,int v)
{
        int i,t;
        if (depth[u] > depth[v]) swap(u,v);
        t = depth[v] - depth[u];
        for (i = 0; i < MAXLOG; i++)
        {
                if (t & (1 << i))
                        v = anc[v][i];
        }
        if (u == v) return u;
        for (i = MAXLOG - 1; i >= 0; i--)
        {
                if (anc[u][i] != anc[v][i])
                {
                        u = anc[u][i];
                        v = anc[v][i];
                }
        }
        return anc[u][0];
}
inline int dist(int x,int y)
{
        return depth[x] + depth[y] - 2 * depth[lca(x,y)];
}
int main() 
{
        
        scanf("%d%d",&n,&m);
        for (i = 1; i < n; i++)
        {
                scanf("%d%d",&u,&v);
                addedge(u,v);
                addedge(v,u);
        }
        dfs(1);
        for (i = 1; i <= m; i++)
        {
                scanf("%d%d%d",&a,&b,&c);
                l1 = lca(a,b);
                l2 = lca(b,c);
                l3 = lca(a,c);
                if (l1 == l2) t = l3;
                else if (l2 == l3) t = l1;
                else t = l2;
                printf("%d %d
",t,dist(a,t) + dist(b,t) + dist(c,t));
        }
        
        return 0;
    
}