new file: P4281.cpp

P4281.cpp

@@ -0,0 +1,60 @@
+#include<bits/stdc++.h>
+using namespace std;
+int n, m;
+vector<int> fri[500005];
+int fa[500005];
+int dep[500005];
+int top[500005];
+int son[500005];
+int cnt[500005];
+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) {
+    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;
+}
+int main() {
+    scanf("%d%d", &n, &m);
+    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, 0);
+    dfs2(1, 1);
+    while(m--) {
+        int x, y, z;
+        scanf("%d%d%d", &x, &y, &z);
+        int l1 = lca(x, y), l2 = lca(x, z), l3 = lca(y, z);
+        int mind = min({dep[l1], dep[l2], dep[l3]});
+        int maxd = max({dep[l1], dep[l2], dep[l3]});
+        if(l1 == l2)
+            printf("%d %d\n", l3, dep[x] + dep[y] + dep[z] - 2 * mind - maxd);
+        else if(l1 == l3)
+            printf("%d %d\n", l2, dep[x] + dep[y] + dep[z] - 2 * mind - maxd);
+        else
+            printf("%d %d\n", l1, dep[x] + dep[y] + dep[z] - 2 * mind - maxd);
+    }
+    return 0;
+}