天天爱跑步

假设现在又一棵树

如果一个人要从 \(3\) 跑到 \(5\),那么如果在 \(2\) 点的观察员要满足 \(w[2] = dep[2] - dep[3]\),如果在点 \(4\) 的观察员要满足 \(w[4] = dep[fa[lca]] - dep[3] + dep[lca] - dep[4]\),简单来说就是如果处于 \(i\) 点的观察员可以观察到,那么要满足 \(w[j] = dep[j] - dep[a]\) 或 \(w[i] = dep[fa[lca]] - dep[a] + dep[lca] - dep[b]\),那么我们可以在点 \(a\) 至 \(lca\) 的链上打个为 \(dep[i] - dep[a]\) 标记,然后在 \(b\) 至 \(son[lca]\) 的链上打个为 \(dep[fa[lca]] - dep[a] + dep[lca] - dep[b]\) 的标记,然后用类似于差分和树上启发式合并即可

#include <bits/stdc++.h>

using namespace std;

const int N = 3e5 + 5;

int n, m, w[N], s[N], t[N], dep[N], dp[N][25], ans[N], fa[N], lc[N];

vector<int> g[N], sum[N];

map<int, int> cnt[3][N];

void dfs1(int u, int f) {
  dep[u] = dep[f] + 1;
  dp[u][0] = f;
  fa[u] = f;
  for (int i = 1; (1 << i) <= dep[u]; i++) {
    dp[u][i] = dp[dp[u][i - 1]][i - 1];
  }
  for (auto v : g[u]) {
    if (v == f) {
      continue;
    }
    dfs1(v, u);
  }
}

int lca(int a, int b) {
  if (dep[a] > dep[b]) {
    swap(a, b);
  }
  for (int i = 20; i >= 0; i--) {
    if (dep[dp[b][i]] >= dep[a]) {
      b = dp[b][i];
    }
  }
  if (a == b) {
    return a;
  }
  for (int i = 20; i >= 0; i--) {
    if (dp[a][i] != dp[b][i]) {
      a = dp[a][i];
      b = dp[b][i];
    }
  }
  return dp[a][0];
}

void dfs(int u, int f) {
  for (auto v : g[u]) {
    if (v == f) {
      continue;
    }
    dfs(v, u);
    for (auto p : {1, 2}) {
      if (cnt[p][v].size() > cnt[p][u].size()) {
        swap(cnt[p][v], cnt[p][u]);
      }
      for (auto cur : cnt[p][v]) {
        cnt[p][u][cur.first] += cur.second;
      }
    }
  }
  ans[u] = cnt[1][u][dep[u] + w[u]] + cnt[2][u][w[u] - dep[u]];
}

int main() {
  cin >> n >> m;
  for (int i = 1, u, v; i < n; i++) {
    cin >> u >> v;
    g[u].push_back(v);
    g[v].push_back(u);
  }
  dfs1(1, 0);
  for (int i = 1; i <= n; i++) {
    cin >> w[i];
  }
  for (int i = 1; i <= m; i++) {
    cin >> s[i] >> t[i];
    int lc = lca(s[i], t[i]);
    int dis = dep[s[i]] + dep[t[i]] - 2 * dep[lc];
    cnt[1][s[i]][dep[s[i]]]++;
    cnt[1][fa[lc]][dep[s[i]]]--;
    cnt[2][t[i]][dis - dep[t[i]]]++;
    cnt[2][lc][dis - dep[t[i]]]--;
  }
  dfs(1, 0);
  for (int i = 1; i <= n; i++) {
    cout << ans[i] << " ";
  }
  return 0;
}

Sum of Tree Distance

虚树和一个简单的树形 \(dp\) 即可,虚树就是建出一个 \(a_i\) 全部相同的数,这样就变得非常好处理

#include <bits/stdc++.h>

using namespace std;

#define int long long

const int N = 3e5 + 5;

struct node {
  int v, w;
};

int n, a[N], dep[N], dfn[N], dcnt, dp[N][25], ans, sz[N], stk[N], x, vis[N];

vector<int> g[N], v[N];

vector<node> new_g[N];

void dfs1(int u, int f) {
  dfn[u] = ++dcnt;
  dep[u] = dep[f] + 1;
  dp[u][0] = f;
  v[a[u]].push_back(u);
  for (int i = 1; (1 << i) <= dep[u]; i++) {
    dp[u][i] = dp[dp[u][i - 1]][i - 1];
  }
  for (auto v : g[u]) {
    if (v == f) {
      continue;
    }
    dfs1(v, u);
  }
}

int lca(int a, int b) {
  if (dep[a] > dep[b]) {
    swap(a, b);
  }
  for (int i = 20; i >= 0; i--) {
    if (dep[dp[b][i]] >= dep[a]) {
      b = dp[b][i];
    }
  }
  if (a == b) {
    return a;
  }
  for (int i = 20; i >= 0; i--) {
    if (dp[a][i] != dp[b][i]) {
      a = dp[a][i];
      b = dp[b][i];
    }
  }
  return dp[a][0];
}

void dfs(int u, int f) {
  sz[u] = (a[u] == x);
  for (auto e : new_g[u]) {
    if (e.v == f) {
      continue;
    }
    dfs(e.v, u);
    sz[u] += sz[e.v];
  }
}

void dfs2(int u, int f) {
  for (auto e : new_g[u]) {
    if (e.v == f) {
      continue;
    }
    ans += e.w * (sz[1] - sz[e.v]) * sz[e.v];
    if (u == 1) {
      //cout << e.w << " " << sz[1] << " " << sz[e.v] << "\n";
    }
    dfs2(e.v, u);
  }
}

void clean(int u, int f) {
  sz[u] = 0;
  for (auto e : new_g[u]) {
    if (e.v == f) {
      continue;
    }
    clean(e.v, u);
  }
  new_g[u].clear();
}

void build() {
  int top = 1;
  stk[top] = 1;
  for (auto cur : v[x]) {
    if (cur == 1) {
      continue;
    }
    int l = lca(cur, stk[top]);
    if (l != stk[top]) {
      while (dfn[l] < dfn[stk[top - 1]]) {
        new_g[stk[top - 1]].push_back({stk[top], abs(dep[stk[top - 1]] - dep[stk[top]])});
        new_g[stk[top]].push_back({stk[top - 1], abs(dep[stk[top - 1]] - dep[stk[top]])});
        top--;
      }
      if (dfn[l] > dfn[stk[top - 1]]) {
        new_g[l].push_back({stk[top], abs(dep[l] - dep[stk[top]])});
        new_g[stk[top]].push_back({l, abs(dep[l] - dep[stk[top]])});
        stk[top] = l;
      }
      else {
        new_g[l].push_back({stk[top], abs(dep[l] - dep[stk[top]])});
        new_g[stk[top]].push_back({l, abs(dep[l] - dep[stk[top]])});
        top--;
      }
    }
    stk[++top] = cur;
  }
  for (int i = 1; i < top; i++) {
    new_g[stk[i]].push_back({stk[i + 1], abs(dep[stk[i]] - dep[stk[i + 1]])});
    new_g[stk[i + 1]].push_back({stk[i], abs(dep[stk[i]] - dep[stk[i + 1]])});
  }
  dfs(1, 0);
  dfs2(1, 0);
  clean(1, 0);
}

signed main() {
  cin >> n;
  for (int i = 1, u, v; i < n; i++) {
    cin >> u >> v;
    g[u].push_back(v);
    g[v].push_back(u);
  }
  for (int i = 1; i <= n; i++) {
    cin >> a[i];
  }
  dfs1(1, 0);
  for (int i = 1; i <= n; i++) {
    if (!vis[a[i]]) {
      x = a[i];
      vis[x] = true;
      build();
    }
  }
  cout << ans;
  return 0;
}

Happy Life in University

我们可以先预处理初对于 \(i\) 节点来说的每个子树内的第一个与他 \(p\) 相等的 \(j\) 存在一个集合里,然后从下往上做操作,对于一个点 \(i\),先将他的集合内的数的子树都加上一个 \(-1\),然后将 \(i\) 的子树全部加上 \(1\) 即可

#include <bits/stdc++.h>

using namespace std;

#define int long long

const int N = 3e5 + 5;

int t, n, a[N], tr[N * 4], lazy[N * 4], dfn[N], dcnt, sz[N], ans, cnt, b[N];

vector<int> g[N], tmp[N];

stack<int> stk[N];

void pushdown(int i, int l, int r) {
  tr[i * 2] += lazy[i];
  lazy[i * 2] += lazy[i];
  tr[i * 2 + 1] += lazy[i];
  lazy[i * 2 + 1] += lazy[i];
  lazy[i] = 0;
}

void modify(int i, int l, int r, int x, int y, int k) {
  if (l > y || r < x) {
    return ;
  }
  if (l >= x && r <= y) {
    tr[i] += k;
    lazy[i] += k;
    return ;
  }
  int mid = (l + r) >> 1;
  pushdown(i, l, r);
  modify(i * 2, l, mid, x, y, k);
  modify(i * 2 + 1, mid + 1, r, x, y, k);
  tr[i] = max(tr[i * 2], tr[i * 2 + 1]);
}

int query(int i, int l, int r, int x, int y) {
  if (l > y || r < x) {
    return 0;
  }
  if (l >= x && r <= y) {
    return tr[i];
  }
  int mid = (l + r) >> 1;
  pushdown(i, l, r);
  return max(query(i * 2, l, mid, x, y), query(i * 2 + 1, mid + 1, r, x, y));
}

void build(int i, int l, int r) {
  if (l == r) {
    tr[i] = 0;
    lazy[i] = 0;
    return ;
  }
  int mid = (l + r) >> 1;
  build(i * 2, l, mid);
  build(i * 2 + 1, mid + 1, r);
  tr[i] = 0, lazy[i] = 0;
}

void dfs1(int u, int f) {
  dfn[u] = ++dcnt;
  sz[u] = 1;
  if (!stk[a[u]].empty()) {
    tmp[stk[a[u]].top()].push_back(u);
  }
  stk[a[u]].push(u);
  for (auto v : g[u]) {
    if (v == f) {
      continue;
    }
    dfs1(v, u);
    sz[u] += sz[v];
  }
  stk[a[u]].pop();
}

void dfs(int u, int f) {
  int maxi1 = 0, maxi2 = 0;
  for (auto v : g[u]) {
    if (v == f) {
      continue;
    }
    dfs(v, u);
  }
  for (auto cur : tmp[u]) {
    modify(1, 1, n, dfn[cur], dfn[cur] + sz[cur] - 1, -1);
  }
  modify(1, 1, n, dfn[u], dfn[u] + sz[u] - 1, 1);
  cnt = 2;
  b[1] = b[2] = 1;
  for (auto v : g[u]) {
    if (v == f) {
      continue;
    }
    int x = query(1, 1, n, dfn[v], dfn[v] + sz[v] - 1);
    b[++cnt] = x;
  }
  sort(b + 1, b + cnt + 1);
  ans = max({ans, b[cnt] * b[cnt - 1]});
}

void Solve() {
  cin >> n;
  for (int i = 2, v; i <= n; i++) {
    cin >> v;
    g[i].push_back(v);
    g[v].push_back(i);
  }
  build(1, 1, n);
  for (int i = 1; i <= n; i++) {
    cin >> a[i];
  }
  dfs1(1, 0);
  dfs(1, 0);
  cout << ans << "\n";
  for (int i = 1; i <= n; i++) {
    g[i].clear();
    tmp[i].clear();
  }
  for (int i = 1; i <= n; i++) {
    while (!stk[i].empty()) {
      stk[i].pop();
    }
  }
  dcnt = 0;
  ans = 0;
}

signed main() {
  ios::sync_with_stdio(0);
  cin.tie(0);
  cin >> t;
  while (t--) {
    Solve();
  }
  return 0;
}