#2124. 「HAOI2015」树上染色

LibreOJ/2124/2124.cpp

@@ -0,0 +1,65 @@
+#include <iostream>
+#include <cstring>
+#include <vector>
+
+using std::cin;
+using std::cout;
+const char endl = '\n';
+
+const int N = 2005;
+
+int n, k, fa[N], siz[N];
+long long f[N][N];
+std::vector<std::pair<int, int>> g[N];
+
+void dfs(int u, int fa) {
+    siz[u] = 1;
+    f[u][0] = f[u][1] = 0;
+
+    for (auto e : g[u]) {
+        int v = e.first,
+            w = e.second;
+
+        if (v == fa) continue;
+
+        dfs(v, u);
+
+        siz[u] += siz[v];
+
+        for (int i = std::min(k, siz[u]); ~i; i--) {
+            if (~f[u][i]) {
+                f[u][i] += f[v][0] + 1ll * siz[v] * (n - k - siz[v]) * w;
+            }
+
+            for (int j = std::min(i, siz[v]); j; j--) {
+                if (~f[u][i - j]) {
+                    f[u][i] = std::max(f[u][i], f[u][i - j] + f[v][j] + 1ll * (j * (k - j) + (siz[v] - j) * (n - k - siz[v] + j)) * w);
+                }
+            }
+        }
+    }
+}
+
+int main() {
+    std::ios::sync_with_stdio(false);
+    cin.tie(nullptr);
+
+    cin >> n >> k;
+
+    k = std::max(k, n - k);
+
+    for (int i = 1, u, v, w; i < n; i++) {
+        cin >> u >> v >> w;
+
+        g[u].push_back(std::make_pair(v, w));
+        g[v].push_back(std::make_pair(u, w));
+    }
+
+    memset(f, 0xff, sizeof(f));
+
+    dfs(1, 0);
+
+    cout << f[1][k] << endl;
+
+    return 0;
+}