P1395 会议

https://www.luogu.com.cn/record/169660795

LibreOJ/144/144.cpp

@@ -0,0 +1,88 @@
+#include <iostream>
+#include <vector>
+
+using std::cin;
+using std::cout;
+const char endl = '\n';
+
+const int N = 1e6 + 5;
+
+int n, m, r, v[N];
+long long f[N];
+int cnt, in[N], out[N];
+std::vector<int> g[N];
+
+int lowbit(int x) {
+    return x & -x;
+}
+
+void add(int x, int y) {
+    for (int i = x; i <= n; i += lowbit(i)) {
+        f[i] += y;
+    }
+}
+
+long long query(int x) {
+    long long res = 0;
+
+    for (int i = x; i; i -= lowbit(i)) {
+        res += f[i];
+    }
+
+    return res;
+}
+
+void dfs(int u, int f) {
+    in[u] = ++cnt;
+    add(cnt, v[u]);
+
+    for (int v : g[u]) {
+        if (v == f) continue;
+
+        dfs(v, u);
+    }
+
+    out[u] = cnt;
+}
+
+int main() {
+    std::ios::sync_with_stdio(false);
+    cin.tie(nullptr);
+
+    cin >> n >> m >> r;
+
+    for (int i = 1; i <= n; i++) {
+        cin >> v[i];
+    }
+
+    for (int i = 1, u, v; i < n; i++) {
+        cin >> u >> v;
+
+        g[u].emplace_back(v);
+        g[v].emplace_back(u);
+    }
+
+    dfs(r, 0);
+
+    while (m--) {
+        int op;
+
+        cin >> op;
+
+        if (op == 1) {
+            int a, x;
+
+            cin >> a >> x;
+
+            add(in[a], x);
+        } else {  // op == 2
+            int a;
+
+            cin >> a;
+
+            cout << query(out[a]) - query(in[a] - 1) << endl;
+        }
+    }
+
+    return 0;
+}

Luogu/B3642/B3642.cpp

@@ -0,0 +1,61 @@
+#include <iostream>
+#include <algorithm>
+#include <iterator>
+
+using std::cin;
+using std::cout;
+const char endl = '\n';
+
+const int N = 1e6 + 5;
+
+int n;
+int lch[N], rch[N];
+int cnt_pre, pre[N],
+    cnt_in, in[N],
+    cnt_post, post[N];
+
+void pre_order(int u) {
+    pre[++cnt_pre] = u;
+
+    if (lch[u]) pre_order(lch[u]);
+    if (rch[u]) pre_order(rch[u]);
+}
+
+void in_order(int u) {
+    if (lch[u]) in_order(lch[u]);
+
+    in[++cnt_in] = u;
+
+    if (rch[u]) in_order(rch[u]);
+}
+
+void post_order(int u) {
+    if (lch[u]) post_order(lch[u]);
+    if (rch[u]) post_order(rch[u]);
+
+    post[++cnt_post] = u;
+}
+
+int main() {
+    std::ios::sync_with_stdio(false);
+    cin.tie(nullptr);
+
+    cin >> n;
+
+    for (int i = 1; i <= n; i++) {
+        cin >> lch[i] >> rch[i];
+    }
+
+    pre_order(1);
+    in_order(1);
+    post_order(1);
+
+    std::copy_n(pre + 1, n, std::ostream_iterator<int>(cout, " "));
+    cout << endl;
+    std::copy_n(in + 1, n, std::ostream_iterator<int>(cout, " "));
+    cout << endl;
+    std::copy_n(post + 1, n, std::ostream_iterator<int>(cout, " "));
+    cout << endl;
+
+    return 0;
+}

Luogu/B4016/B4016.cpp

@@ -0,0 +1,49 @@
+#include <iostream>
+#include <algorithm>
+#include <iterator>
+#include <vector>
+
+using std::cin;
+using std::cout;
+const char endl = '\n';
+
+const int N = 1e5 + 5;
+
+int n, dep[N];
+std::vector<int> g[N];
+
+void dfs(int u, int fa) {
+    dep[u] = dep[fa] + 1;
+
+    for (int v : g[u]) {
+        if (v == fa) continue;
+
+        dfs(v, u);
+    }
+}
+
+int main() {
+    std::ios::sync_with_stdio(false);
+    cin.tie(nullptr);
+
+    cin >> n;
+
+    for (int i = 1, u, v; i < n; i++) {
+        cin >> u >> v;
+
+        g[u].emplace_back(v);
+        g[v].emplace_back(u);
+    }
+
+    dfs(1, 0);
+
+    int u = std::max_element(dep + 1, dep + n + 1) - dep;
+
+    std::fill(std::begin(dep), std::end(dep), 0);
+
+    dfs(u, 0);
+
+    cout << *std::max_element(dep + 1, dep + n + 1) - 1 << endl;
+
+    return 0;
+}

Luogu/P1395/P1395.cpp

@@ -0,0 +1,70 @@
+#include <iostream>
+#include <numeric>
+#include <vector>
+
+using std::cin;
+using std::cout;
+const char endl = '\n';
+
+const int N = 5e4 + 5;
+
+int n;
+int siz[N],     // siz: 子树大小（所有子树上节点数 + 该节点）
+    weight[N];  // weight: 所有子树大小最大值
+int centroid;   // centroid: 重心
+int dep[N];
+std::vector<int> g[N];
+
+void dfs1(int u, int f) {
+    siz[u] = 1;
+    weight[u] = 0;
+
+    for (int v : g[u]) {
+        if (v == f) continue;
+
+        dfs1(v, u);
+
+        siz[u] += siz[v];
+        weight[u] = std::max(weight[u], siz[v]);
+    }
+
+    // 顶上也算一棵子树
+    weight[u] = std::max(weight[u], n - siz[u]);
+
+    // 记录重心
+    if (centroid == 0) centroid = u;
+    else if (weight[u] < weight[centroid]) centroid = u;
+    // 重心相同，取编号小的
+    else if (weight[u] == weight[centroid] && u < centroid) centroid = u;
+}
+
+void dfs2(int u, int f) {
+    dep[u] = dep[f] + 1;
+
+    for (int v : g[u]) {
+        if (v == f) continue;
+
+        dfs2(v, u);
+    }
+}
+
+int main() {
+    std::ios::sync_with_stdio(false);
+    cin.tie(nullptr);
+
+    cin >> n;
+
+    for (int i = 1, u, v; i < n; i++) {
+        cin >> u >> v;
+
+        g[u].emplace_back(v);
+        g[v].emplace_back(u);
+    }
+
+    dfs1(1, 0);
+    dfs2(centroid, 0);
+
+    cout << centroid << ' ' << std::accumulate(dep + 1, dep + 1 + n, 0) - n << endl;
+
+    return 0;
+}