2020.5.23
今天本來信心滿滿去打code+了,結果從彩蛋題就開始懵逼,後來ide壞了,修好以後T1的做法應該是對的,然而segfault了,可能是邊界問題懶得判了。
今天來寫一發樹剖和lca,這個難度都不大,基本都知道該怎麼做,然而這道題要求3節點的lca,然後我寫完就又懵了,這怎麼搞?一次lca大概是log的,但是我起初是用a和b的lca去搞c的lca,然而發現答案錯了。自閉了,去查題解發現,這題的關鍵在於a,b,c三個點的lca有3個,其中兩個必定相同,所以直接就用那個不同的就行了,然後根據depth數組記錄的深度搞出公式就vans了。好吧,我愚鈍了,這題要換我自己來可能真的就比較難了。還有爲什麼那麼多人用tarjan+倍增啊?這麼高深的東西我怎麼可能會呢?還是樹剖方便又容易維護。
代碼:
#include <bits/stdc++.h>
using namespace std;
#define limit (1000000 + 5)//防止溢出
#define INF 0x3f3f3f3f
#define inf 0x3f3f3f3f3f
#define lowbit(i) i&(-i)//一步兩步
#define EPS 1e-6
#define FASTIO ios::sync_with_stdio(false);cin.tie(0);
#define ff(a) printf("%lld\n",a );
#define pi(a,b) pair<a,b>
#define rep(i, a, b) for(int i = a; i <= b ; ++i)
#define per(i, a, b) for(int i = b ; i >= a ; --i)
#define mint(a,b,c) min(min(a,b), c)
#define MOD 998244353
#define FOPEN freopen("C:\\Users\\administrator01\\CLionProjects\\untitled24\\data.txt", "rt", stdin)
typedef long long ll;
typedef unsigned long long ull;
ll read(){
ll sign = 1, x = 0;char s = getchar();
while(s > '9' || s < '0' ){if(s == '-')sign = -1;s = getchar();}
while(s >= '0' && s <= '9'){x = x * 10 + s - '0';s = getchar();}
return x * sign;
}//快讀
void write(ll x){
if(x / 10) write(x / 10);
putchar(x % 10 + '0');
}
int n,k;
int depth[limit], sizes[limit], head[limit<<1] ,cnt, fa[limit],son[limit],top[limit];
struct node{
int to, next;
}edge[limit<<1];
void init(){
memset(head, -1, sizeof(head));
cnt = 0;
}
void add(int u ,int v){
edge[cnt].to = v;
edge[cnt].next = head[u];
head[u] = cnt++;
}
void dfs(int u, int pre){
depth[u] = depth[pre] + 1;
fa[u] = pre;
sizes[u] = 1;
for(int i = head[u]; ~i; i = edge[i].next){
int v = edge[i].to;
if(v != pre) {
dfs(v, u);
sizes[u] += sizes[v];
if (sizes[son[u]] < sizes[v])son[u] = v;
}
}
}
void dfs2(int u, int topp){
top[u] = topp;
if(son[u])dfs2(son[u],topp);
for(int i = head[u]; ~i; i = edge[i].next){
int v= edge[i].to;
if(v != son[u] && v != fa[u])dfs2(v,v);
}
}//二次剖分
int query(int x,int y){
while(top[x] != top[y]){
if(depth[top[x]] >= depth[top[y]])x = fa[top[x]];
else y = fa[top[y]];
}
return depth[x] < depth[y] ? x : y;
}
int main(){
#ifdef LOCAL
FOPEN;
//freopen("C:\\Users\\administrator01\\CLionProjects\\untitled24\\out.txt", "w", stdout);
#endif
n = read(), k = read();
init();
rep(i ,1, n-1){
int x= read(), y = read();
add(x,y);
add(y,x);
}
dfs(1, 0);
dfs2(1,1);
rep( i,1, k){
int a = read(), b = read(), c = read();
int q1 = query(a,b) , q2 = query(b,c) , q3 = query(c,a);
if(q1 == q2)write(q3);
else if(q1 == q3)write(q2);
else write(q1);
printf(" %d\n", depth[a] + depth[b] + depth[c] - depth[q1] - depth[q2] - depth[q3]);
}
return 0;
}