SPOJ 1825 经过不超过K个黑点的树上最长路径 点分治

每一次枚举到重心 按子树中的黑点数SORT一下 启发式合并

 

#include<cstdio>
#include<cstring>
#include<algorithm>
using namespace std;
const int MAXN = 2e6 + 5;
const int MAXM = 2e6 + 5;
int to[MAXM << 1], nxt[MAXM << 1], Head[MAXN], ed = 1;
int cost[MAXM << 1];
const int INF = ~0u >> 1;
inline void addedge(int u, int v, int c)
{
    to[++ed] = v;
    cost[ed] = c;
    nxt[ed] = Head[u];
    Head[u] = ed;
}
inline void ADD(int u, int v, int c)
{
    addedge(u, v, c);
    addedge(v, u, c);
}
inline const int readin()
{
    int r = 0, k = 1;
    char c = getchar();
    for (; c < '0' || c > '9'; c = getchar()) if (c == '-') {
            k = -1;
        }
    for (; c >= '0' && c <= '9'; c = getchar()) {
        r = r * 10 + c - '0';
    }
    return k * r;
}
int n, k, kk, m, anser, cnt, maxdep, summaxdep;
int sz[MAXN], f[MAXN], dep[MAXN], sumsz, root;
bool vis[MAXN];
int ok[MAXN], blasz[MAXN];
int h[MAXN], g[MAXN];
struct node {
    int blaval;
    int id;
} o[MAXN];
bool cmp(node a, node b)
{
    return a.blaval < b.blaval;
}
void getroot(int x, int fa)
{
    sz[x] = 1;
    f[x] = 0;
    for (int i = Head[x]; i; i = nxt[i]) {
        int v = to[i];
        if (v == fa || vis[v]) {
            continue;
        }
        getroot(v, x);
        sz[x] += sz[v];
        f[x] = max(f[x], sz[v]);
    }
    f[x] = max(f[x], sumsz - sz[x]);
    if (f[x] < f[root]) {
        root = x;
    }
}
void update(int x, int blanum, int deep, int fa)
{
    if (blanum > kk) {
        return ;
    }
    h[blanum] = max(h[blanum], deep);
    for (int i = Head[x]; i; i = nxt[i]) {
        int v = to[i];
        if (vis[v] || v == fa) {
            continue;
        }
        update(v, blanum + ok[v], deep + cost[i], x);
    }
}
void getdeep(int x, int fa)
{
    blasz[x] = ok[x];
    for (int i = Head[x]; i; i = nxt[i]) {
        int v = to[i];
        if (v == fa || vis[v]) {
            continue;
        }
        getdeep(v, x);
        blasz[x] += blasz[v];
    }
}
void calc(int x, int d)
{
    cnt = 0;
    for (int i = Head[x]; i; i = nxt[i]) {
        int v = to[i];
        if (vis[v]) {
            continue;
        }
        getdeep(v, x);
        node now;
        now.blaval = blasz[v];
        now.id = i;
        o[++cnt] = now;
    }
}
void solve(int x)
{
    summaxdep = -1;
    kk = k - ok[x];
    int s;
    vis[x] = 1;
    calc(x, 0);
    sort(o + 1, o + cnt + 1, cmp);
    for (int i = 1; i <= cnt; i++) {
        maxdep = -1;
        int depnow = o[i].blaval;
        int v = to[o[i].id];
        int c = cost[o[i].id];
        s = min(depnow, kk);
        for (int j = 0; j <= s; j++) {
            h[j] = -INF;
        }
        update(v, ok[v], c, x);
        if (i == 1) {
            for (int j = 0; j <= s; j++) {
                g[j] = h[j];
            }
        } else {
            for (int j = 0; j <= s; j++) {
                int aim = kk - j;
                aim = min(aim, summaxdep);
                if (h[j] != -INF && g[aim] != -INF) {
                    anser = max(anser, h[j] + g[aim]);
                }
            }
            for (int j = 0; j <= s; j++) {
                g[j] = max(h[j], g[j]);
            }
        }
        summaxdep = s;
        for (int j = 1; j <= summaxdep; j++) {
            g[j] = max(g[j], g[j - 1]);
        }
    }
    anser = max(anser, g[min(kk, summaxdep)]);
    int totsz = sumsz;
    for (int i = Head[x]; i; i = nxt[i]) {
        int v = to[i];
        if (vis[v]) {
            continue;
        }
        root = 0;
        sumsz = sz[v] > sz[x] ? totsz - sz[x] : sz[v];
        getroot(v, 0);
        solve(root);
    }
}
int main()
{
    cnt = anser = 0;
    n = readin(), k = readin(), m = readin();
    for (int now, i = 1; i <= m; i++) {
        now = readin();
        ok[now] = 1;
    }
    int u, v, c;
    for (int i = 1; i < n; i++) {
        u = readin(), v = readin(), c = readin();
        ADD(u, v, c);
    }
    root = 0, sumsz = f[0] = n;
    getroot(1, 0);
    solve(root);
    printf("%d\n", anser);
    return 0;
}