P3398 仓鼠找sugar

R52192514

Luogu/problem/P3398/P3398.cpp

@@ -0,0 +1,69 @@
+#include <bits/stdc++.h>
+
+using namespace std;
+
+int head[100005], ver[200005], nex[200005], tot;
+int fa[100005][30], dep[100005];
+
+inline void addedge(int u, int v) {
+    ver[tot] = v;
+    nex[tot] = head[u];
+    head[u] = tot++;
+}
+
+void dfs(int pre, int cur) {
+    fa[cur][0] = pre;
+    dep[cur] = dep[pre] + 1;
+    for (int i = 1; i <= 25; i++) {
+        fa[cur][i] = fa[fa[cur][i - 1]][i - 1];
+    }
+    for (int i = head[cur]; i != -1; i = nex[i]) {
+        if (!dep[ver[i]]) {
+            dfs(cur, ver[i]);
+        }
+    }
+}
+
+int lca(int u, int v) {
+    if (dep[u] > dep[v]) {
+        swap(u, v);
+    }
+    for (int i = 25; i > -1; i--) {
+        if (dep[fa[v][i]] >= dep[u]) {
+            v = fa[v][i];
+        }
+    }
+    if (u == v) {
+        return v;
+    }
+    for (int i = 25; i > -1; i--) {
+        if (fa[u][i] != fa[v][i]) {
+            u = fa[u][i];
+            v = fa[v][i];
+        }
+    }
+    return fa[u][0];
+}
+
+int main() {
+    int n, t, x, y, a, b, c, d;
+    cin >> n >> t;
+    memset(head, -1, sizeof(head));
+    for (int i = 1; i < n; i++) {
+        cin >> x >> y;
+        addedge(x, y);
+        addedge(y, x);
+    }
+    dfs(0, 1);
+    while (t--) {
+        cin >> a >> b >> c >> d;
+        int x = lca(a, b), y = lca(c, d);
+        if (dep[x] > dep[y]) {
+            swap(x, y);
+            swap(a, c);
+            swap(b, d);
+        }
+        cout << (lca(x, y) == x && (lca(a, y) == y || lca(b, y) == y) ? "Y" : "N") << endl;
+    }
+    return 0;
+}