update

poj/3585.accumulation-degree/main.cc

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+#include <cstdio>
+#include <cstring>
+#include <vector>
+
+// For g++ only
+#define FOREACH(i, a) for (__typeof(a.end()) i = a.begin(); i != a.end(); ++i)
+
+using namespace std;
+
+const int N = 200000;
+
+// dp[i] means the max flow form node i to its subtree in [bottom-up dfs],
+// if sub(i) means the sub nodes of node i, cap(i, j) means the cap of
+// edge i -> j, deg(i) means the degree of node i, then we have:
+// for j in sub(i),
+// dp[i] = dp[i] + cap(i, j), if deg(j) == 1
+//       = dp[i] + min(cap(i, j), dp[j]), if deg(j) > 1
+// In [top-down dfs], we have:
+// for j in sub(i),
+// dp[j] = dp[j] + cap(i, j), if deg(i) == 1
+//       = dp[j] + min(cap(i, j) , dp[i] - min(cap(i, j), dp[j])), if deg(i) > 1
+int dp[N + 1];
+
+vector<pair<int, int> > adj[N + 1];
+
+void bottom_up(int u, int p) {
+  FOREACH(e, adj[u]) {
+    int v = e->first;
+    if (v == p) continue;
+    bottom_up(v, u);
+    if (adj[v].size() == 1)
+      dp[u] += e->second;
+    else
+      dp[u] += min(dp[v], e->second);
+  }
+}
+
+void top_down(int u, int p) {
+  int deg = adj[u].size();
+  FOREACH(e, adj[u]) {
+    int v = e->first;
+    if (v == p) continue;
+    if (deg == 1)
+      dp[v] += e->second;
+    else
+      dp[v] += min(e->second, dp[u] - min(e->second, dp[v]));
+    top_down(v, u);
+  }
+}
+
+int main() {
+  int t, n, u, v, w;
+  scanf("%d", &t);
+  while (t--) {
+    scanf("%d", &n);
+    for (int i = 1; i <= n; i++) adj[i].clear();
+    memset(dp, 0, sizeof(dp));
+    for (int i = 0; i < n - 1; i++) {
+      scanf("%d %d %d", &u, &v, &w);
+      adj[u].push_back(make_pair(v, w));
+      adj[v].push_back(make_pair(u, w));
+    }
+    bottom_up(1, 0);
+    top_down(1, 0);
+    int ans = 0;
+    for (int i = 1; i <= n; i++) ans = max(ans, dp[i]);
+    printf("%d\n", ans);
+  }
+  return 0;
+}