洛谷 P2607 [ZJOI2008]骑士

Posted on Edited on In 
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#include <iostream>
using namespace std;
using LL = long long;
const int N = 1000002;
int n, root;
int h[N], w[N], e[N], ne[N], idx, fa[N];
bool vis[N];
LL f[N][2], ans = 0;
void add(int u, int v) {
    e[++idx] = v, ne[idx] = h[u], h[u] = idx;
}
void dp(int u) {
    vis[u] = true;
    f[u][0] = 0, f[u][1] = w[u];
    for (int i = h[u]; i; i = ne[i]) {
        int v = e[i];
        if (v != root) {
            dp(v);
            f[u][0] += max(f[v][0], f[v][1]);
            f[u][1] += f[v][0];
        } else {
            f[v][1] = -N;
        }
    }
}
void dfs(int u) {
    vis[u] = true;
    root = u;
    while (!vis[fa[root]]) {
        root = fa[root];
        vis[root] = true;
    }
    dp(root);
    LL tmp = max(f[root][0], f[root][1]);
    vis[root] = true;
    root = fa[root];
    dp(root);
    ans += max(tmp, max(f[root][0], f[root][1]));
}
int main() {
    scanf("%d", &n);
    for (int v = 1, u; v <= n; ++v) {
        scanf("%d%d", &w[v], &u);
        add(u, v);
        fa[v] = u;
    }
    for (int i = 1; i <= n; ++i) {
        if (vis[i]) continue;
        dfs(i);
    }
    printf("%lld\n", ans);
    return 0;
}
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#include <iostream>
using namespace std;
using LL = long long;
using PII = pair<int, int>;
const int N = 1000002, M = N * 2;
int n, c, p[N];
PII root[N / 2];
int h[N], w[N], e[M], ne[M], idx;
LL f[N][2], ans;
int find(int x) {
    return x == p[x] ? x : p[x] = find(p[x]);
}
void add(int u, int v) {
    e[++idx] = v, ne[idx] = h[u], h[u] = idx;
}
LL dp(int u, int fa) {
    f[u][0] = 0, f[u][1] = w[u];
    for (int i = h[u]; i; i = ne[i]) {
        int v = e[i];
        if (v == fa) continue;
        dp(v, u);
        f[u][0] += max(f[v][0], f[v][1]);
        f[u][1] += f[v][0];
    }
    return f[u][0];
}
int main() {
    scanf("%d", &n);
    for (int i = 1; i <= n; ++i) p[i] = i;
    for (int u = 1, v; u <= n; ++u) {
        scanf("%d%d", &w[u], &v);
        if (find(u) != find(v)) {
            p[find(u)] = find(v);
            add(u, v), add(v, u);
        } else {
            root[c++] = {u, v};
        }
    }
    for (int i = 0; i < c; ++i) {
        auto [u, v] = root[i];
        ans += max(dp(u, 0), dp(v, 0));
    }
    printf("%lld\n", ans);
    return 0;
}