P4189 [CTSC2010]星际旅行

https://www.luogu.com.cn/record/100786864

Luogu/P4189/P4189.cpp

@@ -0,0 +1,84 @@
+#include <iostream>
+#include <vector>
+
+using std::cin;
+using std::cout;
+const char endl = '\n';
+
+const int N = 50005;
+
+int n, h[N], son[N], ans[N], res;
+std::vector<int> g[N];
+
+void dfs1(int u, int f) {
+    for (int v : g[u]) {
+        if (v == f) continue;
+
+        dfs1(v, u);
+
+        int x = std::min(h[u], h[v]);
+
+        h[u] -= x, h[v] -= x;
+        res += x * 2;
+
+        if (h[v]) son[u] = v;
+    }
+}
+
+void dfs2(int u, int f) {
+    ans[u] = res;
+
+    for (int v : g[u]) {
+        if (v == f) continue;
+
+        if (h[u]) {
+            h[u]--, res++;
+
+            dfs2(v, u);
+
+            h[u]++, res--;
+        } else if (son[v]) {
+            h[son[v]]--, res++;
+
+            dfs2(v, u);
+
+            h[son[v]]++, res--;
+        } else {
+            h[v]++, res--;
+
+            dfs2(v, u);
+
+            h[v]--, res++;
+        }
+    }
+}
+
+int main() {
+    std::ios::sync_with_stdio(false);
+    cin.tie(nullptr);
+
+    cin >> n;
+
+    for (int i = 1; i <= n; i++) {
+        cin >> h[i];
+    }
+
+    for (int i = 1, x, y; i < n; i++) {
+        cin >> x >> y;
+
+        h[++x]--, h[++y]--;
+        g[x].emplace_back(y);
+        g[y].emplace_back(x);
+
+        res += 2;
+    }
+
+    dfs1(1, 0);
+    dfs2(1, 0);
+
+    for (int i = 1; i <= n; i++) {
+        cout << ans[i] << endl;
+    }
+
+    return 0;
+}