BZOJ1787/Luogu4281: [Ahoi2008]Meet 紧急集合

画画图可知，三点(lca)必有两相同，(a,b,c)距离为(dis_a + dis_b + dis_c - dis_{lca(a,b)} - dis_{lca(b,c)} - dis_{lca(a,c)})

#include <iostream>
#include <cstdio>
#include <cstring>
#include <algorithm>
#include <cmath>
#define R(a,b,c) for(register int  a = (b); a <= (c); ++ a)
#define nR(a,b,c) for(register int  a = (b); a >= (c); -- a)
#define Max(a,b) ((a) > (b) ? (a) : (b))
#define Min(a,b) ((a) < (b) ? (a) : (b))
#define Fill(a,b) memset(a, b, sizeof(a))
#define Swap(a,b) a^=b^=a^=b
#define ll long long
#define ON_DEBUG

#ifdef ON_DEBUG

#define D_e_Line printf("

----------

")
#define D_e(x)  cout << #x << " = " << x << endl
#define Pause() system("pause")

#else

#define D_e_Line ;

#endif

struct ios{
    template<typename ATP>ios& operator >> (ATP &x){
        x = 0; int f = 1; char c;
        for(c = getchar(); c < '0' || c > '9'; c = getchar()) if(c == '-')  f = -1;
        while(c >= '0' && c <= '9') x = x * 10 + (c ^ '0'), c = getchar();
        x*= f;
        return *this;
    }
}io;
using namespace std;

const int N = 500007;

struct Edge{
	int nxt, pre, w;
}e[N << 1];
int head[N], cntEdge;
inline void add(int u, int v, int w){
	e[++cntEdge] = (Edge){head[u], v, w}, head[u] = cntEdge;
}

int dis[N];
int fa[N], son[N], siz[N], dep[N];
inline void DFS_First(int u, int father){
	fa[u] = father, dep[u] = dep[father] + 1, siz[u] = 1;
	for(register int i = head[u]; i; i = e[i].nxt){
		int v = e[i].pre;
		if(v == father) continue;
		dis[v] = dis[u] + e[i].w;
		DFS_First(v, u);
		siz[u] += siz[v];
		if(!son[u] || siz[v] > siz[son[u]]){
			son[u] = v;
		}
	}
}
int dfn[N], dfnIdx, top[N];
inline void DFS_Second(int u, int ancester){
	top[u] = ancester, dfn[u] = ++dfnIdx;
	if(!son[u]) return;
	DFS_Second(son[u], ancester);
	for(register int i = head[u]; i; i = e[i].nxt){
		int v = e[i].pre;
		if(v != son[u] && v != fa[u]){
			DFS_Second(v, v);
		}
	}
}
inline int LCA(int x, int y){
	while(top[x] != top[y]){
		if(dep[top[x]] < dep[top[y]]) Swap(x, y);
		x = fa[top[x]];
	}
	return dep[x] < dep[y] ? x : y;
}

int main(){
	int n, Ques;
	io >> n >> Ques;
	R(i,2,n){
		int u, v;
		io >> u >> v;
		add(u, v, 1);
		add(v, u, 1);
	}
	
	DFS_First(1, 0);
	DFS_Second(1, 1);
	
	while(Ques--){
		int a, b, c;
		io >> a >> b >> c;
		int A = LCA(a, b), B = LCA(b, c), C = LCA(a, c);
//		int disA = dis[a] + dis[b] - (dis[A] << 1);
//		int disB = dis[b] + dis[c] - (dis[B] << 1);
//		int disC = dis[a] + dis[c] - (dis[C] << 1);
		int pos;
		if(A == B) pos = C;
		else if(B == C) pos = A;
		else pos = B;
		printf("%d %d
", pos, dis[a] + dis[b] + dis[c] - dis[A] - dis[B] - dis[C]);
	}
	
	return 0;
}