#1911. M 弟娃（magic）

https://sjzezoj.com/submission/69072

S2OJ/1911/1911.cpp

@@ -0,0 +1,175 @@
+#include <iostream>
+#include <vector>
+
+using std::cin;
+using std::cout;
+const char endl = '\n';
+
+const int N = 3e5 + 5;
+
+int n, m;
+int id[N], rid[N], fa[N], dep[N], siz[N], son[N], top[N];
+std::vector<int> g[N];
+
+struct node {
+    int l, r, m, d;
+
+    node(const int &_l = 0, const int &_r = 0)
+        : l(_l), r(_r), m(0), d(0) {}
+} tr[N << 2];
+
+void dfs1(int u, int f) {
+    fa[u] = f;
+    dep[u] = dep[f] + 1;
+    siz[u] = 1;
+
+    for (int v : g[u]) {
+        if (v == f) continue;
+
+        dfs1(v, u);
+        siz[u] += siz[v];
+
+        if (siz[son[u]] < siz[v]) son[u] = v;
+    }
+}
+
+void dfs2(int u, int t) {
+    static int cnt = 0;
+
+    rid[id[u] = ++cnt] = u;
+    top[u] = t;
+
+    if (son[u]) dfs2(son[u], t);
+
+    for (int v : g[u]) {
+        if (v == fa[u] || v == son[u]) continue;
+
+        dfs2(v, v);
+    }
+}
+
+void pushup(int u) {
+    tr[u].m = std::max(tr[u << 1].m, tr[u << 1 | 1].m);
+}
+
+void pushdown(int u) {
+    if (!tr[u].d) return;
+
+    tr[u << 1].m += tr[u].d;
+    tr[u << 1].d += tr[u].d;
+
+    tr[u << 1 | 1].m += tr[u].d;
+    tr[u << 1 | 1].d += tr[u].d;
+
+    tr[u].d = 0;
+}
+
+void build(int u, int l, int r) {
+    tr[u] = node(l, r);
+
+    if (l == r) return;
+
+    int mid = (l + r) >> 1;
+
+    build(u << 1, l, mid);
+    build(u << 1 | 1, mid + 1, r);
+
+    pushup(u);
+}
+
+void modify(int u, int l, int r, int x) {
+    if (l <= tr[u].l && tr[u].r <= r) {
+        tr[u].m += x;
+        tr[u].d += x;
+
+        return;
+    }
+
+    int mid = (tr[u].l + tr[u].r) >> 1;
+
+    pushdown(u);
+
+    if (l <= mid) modify(u << 1, l, r, x);
+    if (r > mid) modify(u << 1 | 1, l, r, x);
+
+    pushup(u);
+}
+
+int query(int u, int l, int r) {
+    if (l <= tr[u].l && tr[u].r <= r) return tr[u].m;
+
+    int mid = (tr[u].l + tr[u].r) >> 1;
+
+    pushdown(u);
+
+    int res = 0;
+
+    if (l <= mid) res = std::max(res, query(u << 1, l, r));
+    if (r > mid) res = std::max(res, query(u << 1 | 1, l, r));
+
+    return res;
+}
+
+void modify_tree(int u, int d) {
+    modify(1, id[u], id[u] + siz[u] - 1, d);
+}
+
+int lca(int u, int v) {
+    while (top[u] != top[v]) {
+        if (dep[top[u]] < dep[top[v]]) std::swap(u, v);
+        u = fa[top[u]];
+    }
+
+    return dep[u] < dep[v] ? u : v;
+}
+
+int find(int u, int v) {
+    while (top[u] != top[v]) {
+        if (fa[top[v]] == u) return top[v];
+
+        v = fa[top[v]];
+    }
+
+    return son[u];
+}
+
+int main() {
+    std::ios::sync_with_stdio(false);
+    cin.tie(nullptr);
+
+    cin >> n >> m;
+
+    for (int i = 1, x, y; i < n; i++) {
+        cin >> x >> y;
+
+        g[x].emplace_back(y);
+        g[y].emplace_back(x);
+    }
+
+    dfs1(1, 1);
+    dfs2(1, 1);
+    build(1, 1, n);
+
+    for (int i = 1, x, y; i <= m; i++) {
+        cin >> x >> y;
+
+        if (x != y) {
+            int g = lca(x, y);
+
+            if (dep[x] < dep[y]) std::swap(x, y);
+
+            if (y == g) {  // x 在以 y 为根的子树内
+                modify_tree(find(y, x), -1);
+                modify_tree(x, 1);
+            } else {
+                modify_tree(1, -1);
+                modify_tree(x, 1);
+                modify_tree(y, 1);
+            }
+        }
+
+        cout << i + query(1, 1, n) << endl;
+    }
+
+    return 0;
+}