new file: P3128.cpp

P3128.cpp

@@ -0,0 +1,71 @@
+#include<bits/stdc++.h>
+using namespace std;
+int n, k;
+vector<int> fri[100005];
+int cnt[100005];
+int fa[100005];
+int son[100005];
+int dfn[100005];
+int top[100005];
+int dep[100005];
+int nowdfn;
+int ans[100005];
+void dfs1(int now, int from) {
+    cnt[now] = 1;
+    for(int i : fri[now]) {
+        if(i == from) continue;
+        fa[i] = now;
+        dep[i] = dep[now] + 1;
+        dfs1(i, now);
+        cnt[now] += cnt[i];
+        if(cnt[son[now]] < cnt[i]) son[now] = i;
+    }
+}
+void dfs2(int now, int from) {
+    dfn[now] = ++nowdfn;
+    top[now] = from;
+    if(son[now]) dfs2(son[now], from);
+    for(int i : fri[now]) {
+        if(i == fa[now] || i == son[now]) continue;
+        dfs2(i, i);
+    }
+}
+int lca(int a, int b) {
+    while(top[a] != top[b]) {
+        if(dep[top[a]] < dep[top[b]]) swap(a, b);
+        a = fa[top[a]];
+    }
+    if(dep[a] < dep[b]) swap(a, b);
+    return b;
+}
+void dfsadd(int now, int from) {
+    for(int i : fri[now]) {
+        if(i == from) continue;
+        dfsadd(i, now);
+        ans[now] += ans[i];
+    }
+}
+int main() {
+    scanf("%d%d", &n, &k);
+    for(int i = 1, u, v; i < n; ++i) {
+        scanf("%d%d", &u, &v);
+        fri[u].push_back(v);
+        fri[v].push_back(u);
+    }
+    dfs1(1, -1);
+    dfs2(1, 1);
+    while(k--) {
+        int u, v;
+        scanf("%d%d", &u, &v);
+        int w = lca(u, v);
+        ans[u]++;
+        ans[v]++;
+        ans[w]--;
+        if(fa[w]) ans[fa[w]]--;
+    }
+    dfsadd(1, -1);
+    int maxans = 0;
+    for(int i = 1; i <= n; ++i) maxans = max(maxans, ans[i]);
+    printf("%d\n", maxans);
+    return 0;
+}