法一:dsu
#include <bits/stdc++.h>
using ll = long long;
using namespace std;
const int N = 100010;
struct node {
int v, nxt;
}e[N * 2];
int h[N], idx;
int p[N], n, w[N];
int dp[N][2];
inline void add(int u, int v) {
e[++idx] = {v, h[u]}, h[u] = idx;
}
int find(int x) {
return x == p[x] ? p[x] : p[x] = find(p[x]);
}
void dfs(int u, int fa) {
std::cerr << u << " " << fa << "\n";
dp[u][1] = w[u], dp[u][0] = 0;
for (int i = h[u]; i; i = e[i].nxt) {
int v = e[i].v;
if (v == fa) continue;
dfs(v, u);
dp[u][1] += dp[v][0];
dp[u][0] += std::max(dp[v][0], dp[v][1]);
}
}
signed main() {
std::cin.tie(nullptr)->sync_with_stdio(false);
cin >> n;
for (int i = 1; i <= n; i++) {
std::cin >> w[i];
p[i] = i;
}
int s, t;
for (int i = 1; i <= n; i++) {
int u, v;
std::cin >> u >> v;
u++, v++;
if (find(u) == find(v)) {
s = u;
t = v;
continue;
}
add(u, v), add(v, u);
p[find(u)] = find(v);
}
double k;
cin >> k;
int ans = 0;
// cerr << ans << " " << s << ' ' << t << "\n";
dfs(s, 0); ans = dp[s][0];
dfs(t, 0); ans = max(ans, dp[t][0]);
// printf("%.1lf\n", ans * k);
cout << fixed << setprecision(1) << ans * k << "\n";
return 0 ^ 0;
}
基环树 + dp
#include <bits/stdc++.h>
using ll = long long;
using namespace std;
const int N = 100010;
const int inf = 0x3f3f3f3f;
struct node {
int v, nxt;
}e[N * 2];
int h[N], idx, n, b;
int a[N], d[N];
int c[N], ptr;
bool cir[N];
int dp[N][2], ndp[N][2];
void add(int u, int v) {
e[++idx] = {v, h[u]}, h[u] = idx;
}
void dfs1(int u, int fa) {
for (int i = h[u]; i; i = e[i].nxt) {
int v = e[i].v;
if (v == fa || cir[v]) continue;
if (d[v] == 2) {
c[++ptr] = v, cir[v] = true;
dfs1(v, u);
break;
}
}
}
void dfs(int u, int fa) {
dp[u][1] = a[u];
for (int i = h[u]; i; i = e[i].nxt) {
int v = e[i].v;
if (v == fa || cir[v]) continue;
dfs(v, u);
dp[u][0] += max(dp[v][0], dp[v][1]);
dp[u][1] += dp[v][0];
}
}
signed main() {
std::cin.tie(nullptr)->sync_with_stdio(false);
cin >> n;
for (int i = 1; i <= n; i++) {
cin >> a[i];
}
for (int i = 1; i <= n; i++) {
int u, v;
cin >> u >> v;
u++, v++;
d[u]++, d[v]++;
add(u, v), add(v, u);
}
double k;
cin >> k;
queue<int> q;
for (int i = 1; i <= n; i++)
if (d[i] == 1)
q.push(i);
while(q.size()) {
int u = q.front();
q.pop();
for (int i = h[u]; i; i = e[i].nxt) {
int v = e[i].v;
if (--d[v] == 1)
q.push(v);
}
}
for (int i = 1; i <= n; i++) {
if (d[i] == 2) {
c[++ptr] = i, cir[i] = true;
dfs1(i, 0);
break;
}
}
for (int i = 1; i <= ptr; i++) {
dfs(c[i], 0);
}
for (int i = 0; i <= n; i++) {
ndp[i][0] = ndp[i][1] = -inf;
}
ndp[1][0] = dp[c[1]][0];
for (int i = 2; i <= ptr; i++) {
ndp[i][1] = ndp[i - 1][0] + dp[c[i]][1];
ndp[i][0] = max(ndp[i - 1][0], ndp[i - 1][1]) + dp[c[i]][0];
}
int ans = max(ndp[ptr][0], ndp[ptr][1]);
for (int i = 0; i <= n; i++) {
ndp[i][0] = ndp[i][1] = -inf;
}
ndp[1][1] = dp[c[1]][1];
for (int i = 2; i <= ptr; i++) {
ndp[i][1] = ndp[i - 1][0] + dp[c[i]][1];
ndp[i][0] = max(ndp[i - 1][0], ndp[i - 1][1]) + dp[c[i]][0];
}
ans = max(ans, ndp[ptr][0]);
cout << fixed << setprecision(1) << k * ans << "\n";
return 0 ^ 0;
}
原文地址:http://www.cnblogs.com/Haven-/p/16919581.html
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