Merge pull request #1304 from AlgorithmWithGod/khj20006

[20251103] BOJ / P3 / 도시 정비 / 권혁준

Author: ShinHeeEul

khj20006/202511/03 BOJ P3 도시 정비.md

@@ -0,0 +1,49 @@
+```cpp
+#include <bits/stdc++.h>
+using namespace std;
+using ll = long long;
+
+int N;
+vector<vector<int>> v(1000001);
+ll inmx[1000001]{}, outmx[1000001]{}, ex[1000001]{}, val[1000001]{}, a[1000001]{};
+ll ans = 0;
+
+void dfs1(int n, int p) {
+	inmx[n] = a[n];
+	ll mx1 = 0, mx2 = 0;
+	for (int i : v[n]) if (i != p) {
+		dfs1(i, n);
+		if (inmx[i] > mx1) mx2 = mx1, mx1 = inmx[i];
+		else if (inmx[i] > mx2) mx2 = inmx[i];
+		inmx[n] = max(inmx[n], inmx[i]);
+	}
+	for (int i : v[n]) if (i != p) {
+		if (inmx[i] == mx1) ex[i] = mx2;
+		else ex[i] = mx1;
+		val[n] += inmx[i];
+	}
+}
+
+void dfs2(int n, int p) {
+	outmx[n] = max({ outmx[p], (ll)a[p], ex[n] });
+	ans = max(ans, val[n] + outmx[n]);
+	for (int i : v[n]) if (i != p) dfs2(i, n);
+}
+
+int main() {
+	cin.tie(0)->sync_with_stdio(0);
+
+	cin >> N;
+	for (int i = 1; i <= N; i++) cin >> a[i];
+	for (int i = 1, c, d; i < N; i++) {
+		cin >> c >> d;
+		v[c].push_back(d);
+		v[d].push_back(c);
+	}
+	dfs1(1, 0);
+	dfs2(1, 0);
+
+	cout << ans;
+
+}
+```