H1008. 【模板】最近公共祖先

https://hydro.ac/record/61acb81d0ca64e079359e31f

Hydro/system/H1008/H1008.cpp

@@ -0,0 +1,62 @@
+#include <bits/stdc++.h>
+
+using std::cin;
+using std::cout;
+using std::endl;
+
+int n, q, u, v, fa[500005][20], dep[500005];
+std::vector<int> g[500005];
+
+void bfs(int root) {
+    memset(dep, 0x3f, sizeof(dep));
+    std::queue<int> q;
+    dep[0] = 0;
+    dep[root] = 1;
+    q.push(root);
+    while (!q.empty()) {
+        int t = q.front();
+        q.pop();
+        for (int v : g[t]) {
+            if (dep[v] > dep[t] + 1) {
+                dep[v] = dep[t] + 1;
+                q.push(v);
+                fa[v][0] = t;
+                for (int k = 1; k < 20; k++) {
+                    fa[v][k] = fa[fa[v][k - 1]][k - 1];
+                }
+            }
+        }
+    }
+}
+
+int lca(int a, int b) {
+    if (dep[a] < dep[b]) std::swap(a, b);
+    for (int k = 19; k >= 0; k--) {
+        if (dep[fa[a][k]] >= dep[b]) {
+            a = fa[a][k];
+        }
+    }
+    if (a == b) return a;
+    for (int k = 19; k >= 0; k--) {
+        if (fa[a][k] != fa[b][k]) {
+            a = fa[a][k];
+            b = fa[b][k];
+        }
+    }
+    return fa[a][0];
+}
+
+int main() {
+    scanf("%d%d", &n, &q);
+    for (int i = 1; i < n; i++) {
+        scanf("%d%d", &u, &v);
+        g[u].push_back(v);
+        g[v].push_back(u);
+    }
+    bfs(1);
+    while (q--) {
+        scanf("%d%d", &u, &v);
+        printf("%d\n", lca(u, v));
+    }
+    return 0;
+}