Luogu 3320 [SDOI2015]寻宝游戏

#include <cstdio>
#include <cstring>
#include <set>
using namespace std;
typedef long long ll;

const int N = 1e5 + 5;
const int Lg = 20;

int n, qn, tot = 0, head[N];
int dep[N], fa[N][Lg], dfsc = 0, id[N], mp[N];
ll ans = 0LL, dis[N];
bool ex[N];
set <int> s;

struct Edge {
    int to, nxt;
    ll val;
} e[N << 1];

inline void add(int from, int to, ll val) {
    e[++tot].to = to;
    e[tot].val = val;
    e[tot].nxt = head[from];
    head[from] = tot;
}  

template <typename T>
inline void read(T &X) {
    X = 0; char ch = 0; T op = 1;
    for(; ch > ‘9‘ || ch < ‘0‘; ch = getchar())
        if(ch == ‘-‘) op = -1;
    for(; ch >= ‘0‘ && ch <= ‘9‘; ch = getchar())
        X = (X << 3) + (X << 1) + ch - 48;
    X *= op;
}

void dfs(int x, int fat, int depth, ll nowDis) {
    fa[x][0] = fat, dep[x] = depth, dis[x] = nowDis;
    id[x] = ++dfsc, mp[id[x]] = x;
    for(int i = 1; i <= 18; i++)
        fa[x][i] = fa[fa[x][i - 1]][i - 1];
    for(int i = head[x]; i; i = e[i].nxt) {
        int y = e[i].to;
        if(y == fat) continue;
        dfs(y, x, depth + 1, nowDis + e[i].val);
    }
}

inline void swap(int &x, int &y) {
    int t = x; x = y; y = t;
}

inline int getLca(int x, int y) {
    if(dep[x] < dep[y]) swap(x, y);
    for(int i = 18; i >= 0; i--)
        if(dep[fa[x][i]] >= dep[y])
            x = fa[x][i];
    if(x == y) return x;
    for(int i = 18; i >= 0; i--)
        if(fa[x][i] != fa[y][i])
            x = fa[x][i], y = fa[y][i];
    return fa[x][0];
}

inline ll getDis(int x, int y) {
    int z = getLca(x, y);
    return dis[x] + dis[y] - 2 * dis[z];
}

int main() {
    read(n), read(qn);
    for(int x, y, i = 1; i < n; i++) {
        read(x), read(y);
        ll v; read(v);
        add(x, y, v), add(y, x, v); 
    }
    dfs(1, 0, 1, 0LL);
    
/*    for(int i = 1; i <= n; i++) 
        printf("%d ", id[i]);
    printf("\n");    */
    
    for(int x, cnt = 0; qn--; ) {
        read(x);
        if(!ex[x]) {
            ex[x] = 1;
            s.insert(id[x]);
            ++cnt;
            if(cnt == 1) {
                puts("0");
                continue;
            }
            set <int> :: iterator it = s.find(id[x]), it2 = it;
            if(it == s.begin()) it = s.end();
            int lst = *(--it);
            it = s.find(id[x]);
            int nxt = 0;
            if((++it2) == s.end()) nxt = *(s.begin());
            else nxt = *(++it);
            ans += getDis(mp[lst], x) + getDis(mp[nxt], x) - getDis(mp[lst], mp[nxt]);
        } else {
            ex[x] = 0;
            --cnt;
            if(cnt == 0) {
                puts("0");
                s.erase(id[x]);
                continue;
            }
            set <int> :: iterator it = s.find(id[x]), it2 = it;
            if(it == s.begin()) it = s.end();
            int lst = *(--it);
            it = s.find(id[x]);
            int nxt = 0;
            if((++it2) == s.end()) nxt = *(s.begin());
            else nxt = *(++it);
            ans -= getDis(mp[lst], x) + getDis(mp[nxt], x) - getDis(mp[lst], mp[nxt]);            
            s.erase(id[x]);
        }
        printf("%lld\n", ans);
    }
    
    return 0;
}