(mathcal{A})
重建计划
#include <bits/stdc++.h>
using namespace std;
//namespace cyl {
const int N = (int)1e5 + 5;
const double eps = 1e-4;
double mid;
int siz[N], mxs[N], cnt, ans = 0, n, L, U, S, rt, num[N], q[N], o;
bool vis[N], flag;
vector<vector<pair<int, double> > > son[N];
vector<pair<int, double> > *c, p, np;
vector<pair<int, int> > G[N];
vector<int> E[N];
void getrt(int u, int fa) {
siz[u] = 1, mxs[u] = 0;
for (auto x : G[u])
if (!vis[x.first] && x.first != fa) {
getrt(x.first, u);
siz[u] += siz[x.first];
mxs[u] = max(mxs[u], siz[x.first]);
}
mxs[u] = max(mxs[u], S - siz[u]);
if (rt == -1 || mxs[rt] > mxs[u]) rt = u;
}
void dfs(int u, int fa, int t, double d) {
c->push_back(make_pair(t, d));
for (auto x : G[u])
if (!vis[x.first] && x.first != fa)
dfs(x.first, u, t + 1, d + x.second);
}
void div(int u) {
vis[u] = 1;
son[u].push_back(*(new vector<pair<int, double> >));
for (auto x : G[u])
if (!vis[x.first]) {
son[u].push_back(*(new vector<pair<int, double> >));
c = &son[u][++num[u]];
dfs(x.first, 0, 1, x.second);
sort(c->begin(), c->end());
}
sort(son[u].begin(), son[u].end(), [](vector<pair<int, double> > &a, vector<pair<int, double> > &b) { return a.size() < b.size(); });
for (auto x : G[u])
if (!vis[x.first]) {
S = siz[x.first], rt = -1, getrt(x.first, 0);
E[u].push_back(rt);
div(rt);
}
}
void work(int u) {
if (flag) return;
p.clear();
p.push_back(make_pair(0, 0));
for (int i = 1; i <= num[u]; ++i) {
int l = 1, r = 0, j = 0;
for (int i2 = son[u][i].size() - 1; i2 >= 0; --i2) {
auto x = son[u][i][i2];
while (j < p.size() && p[j].first + x.first <= U) {
while (l <= r && p[j].second - mid * p[j].first >= p[q[r]].second - mid * p[q[r]].first) --r;
q[++r] = j++;
}
while (l <= r && p[q[l]].first + x.first < L) ++l;
if (l <= r && p[q[l]].second - mid * p[q[l]].first + x.second - mid * x.first > -eps) {
flag = 1;
break;
}
}
np.clear();
for (int j = 0, k = 0; j < p.size() || k < son[u][i].size(); )
if (k == son[u][i].size() || j < p.size() && p[j] < son[u][i][k])
np.push_back(p[j++]);
else
np.push_back(son[u][i][k++]);
swap(p, np);
}
for (auto v : E[u]) work(v);
}
bool check() {
flag = 0;
work(o);
return flag;
}
int main() {
scanf("%d%d%d", &n, &L, &U);
for (int i = 1, u, v, w; i < n; ++i) {
scanf("%d%d%d", &u, &v, &w);
G[u].push_back(make_pair(v, w));
G[v].push_back(make_pair(u, w));
}
S = n, rt = -1, getrt(1, 0);
o = rt;
div(rt);
double l = 0, r = 1e6;
while (r - l >= eps) {
mid = (l + r) / 2;
if (check()) l = mid;
else r = mid;
}
printf("%.3lf
", l);
return 0;
}
//} int main() { return cyl::main(); }
(mathcal{B})
树分块，大概有这样的一些方法：
- 王室联邦分块法：可以保证每个块的大小和直径都不超过2√N−1，但是不保证块联通
- DFS序分块法：首先是好写（毕竟转化成了序列问题），严格保证块大小√N，但是不保证直径，也不保证联通。处理子树信息比较方便
- size分块：检查当前节点的父亲所在块的大小，如果小于√N就把当前节点加入进去，不然新开块。块大小最坏√N，保证块内联通，还保证直径，多么优美啊可惜不能保证块个数（一个菊花图就死了）(摘自https://www.cnblogs.com/hua-dong/p/8275227.html)
- 按dep模块大小分类（代码2）
糖果公园
#include <bits/stdc++.h>
using namespace std;
//namespace cyl {
const int N = (int)1e5 + 5;
int sub[N], fa[N], son[N], stk[N], top[N], siz, tp, bid[N], dep[N], cnt[N], w[N], val[N], c[N], qx[N], qy[N], qk[N], qu[N], qv[N], qz[N];
bool vis[N];
int n, m, q, cc[N], ccnt, qcnt, id[N], oooo;
long long ret, ans[N];
vector<int> G[N];
int read() {
int x = 0, f = 1; char c = getchar();
while (c > -1 && c < '0' || c > '9') { if (c == '-') f = -1; c = getchar(); }
if (c == -1) return 0;
while (c >= '0' && c <= '9') x = x * 10 + c - 48, c = getchar();
return x * f;
}
void dfs1(int u) {
int bt = tp;
stk[++tp] = u;
// if (tp >= siz) {
// ++oooo;
// for (int i = 1; i <= tp; ++i) bid[stk[i]] = oooo;
// tp = 0;
// }
sub[u] = 1;
int t = -1;
for (int v : G[u])
if (v != fa[u]) {
dep[v] = dep[u] + 1;
fa[v] = u;
dfs1(v);
if (tp - bt > siz) {
++oooo;
while (tp != bt) bid[stk[tp--]] = oooo;
}
sub[u] += sub[v];
if (sub[v] > t) {
t = sub[v];
son[u] = v;
}
}
}
void dfs2(int u, int t) {
top[u] = t;
if (son[u] == 0) return;
dfs2(son[u], t);
for (int v : G[u])
if (v != fa[u] && v != son[u])
dfs2(v, v);
}
int lca(int u, int v) {
while (top[u] != top[v]) {
if (dep[top[u]] < dep[top[v]]) swap(u, v);
u = fa[top[u]];
}
return dep[u] < dep[v] ? u : v;
}
void ins(int u) {
++cnt[c[u]];
ret += 1ll * w[cnt[c[u]]] * val[c[u]];
}
void del(int u) {
ret -= 1ll * w[cnt[c[u]]] * val[c[u]];
--cnt[c[u]];
}
void ver1(int k) {
if (vis[qx[k]]) del(qx[k]);
c[qx[k]] = qy[k];
if (vis[qx[k]]) ins(qx[k]);
}
void ver2(int k) {
if (vis[qx[k]]) del(qx[k]);
c[qx[k]] = qz[k];
if (vis[qx[k]]) ins(qx[k]);
}
void update(int u) {
if (vis[u]) vis[u] = 0, del(u);
else vis[u] = 1, ins(u);
}
void work(int u, int v) {
while (u != v) {
if (dep[u] < dep[v]) swap(u, v);
update(u);
u = fa[u];
}
}
int main() {
n = read(), m = read(), q = read(), siz = pow(n, 0.6666);
for (int i = 1; i <= m; ++i) val[i] = read();
for (int i = 1; i <= n; ++i) w[i] = read();
for (int i = 1; i < n; ++i) {
int u = read(), v = read();
G[u].push_back(v);
G[v].push_back(u);
}
for (int i = 1; i <= n; ++i) cc[i] = c[i] = read();
dfs1(1);
dfs2(1, 1);
++oooo;
for (int i = 1; i <= tp; ++i) bid[stk[i]] = oooo;
for (int i = 1; i <= q; ++i) {
int op = read();
if (op == 0) {
qx[++ccnt] = read(), qy[ccnt] = read();
qz[ccnt] = cc[qx[ccnt]];
cc[qx[ccnt]] = qy[ccnt];
} else {
qu[++qcnt] = read(), qv[qcnt] = read();
qk[qcnt] = ccnt;
id[qcnt] = qcnt;
}
}
sort(id + 1, id + qcnt + 1, [](int x, int y) {
return bid[qu[x]] < bid[qu[y]] || bid[qu[x]] == bid[qu[y]] && bid[qv[x]] < bid[qv[y]] ||
bid[qu[x]] == bid[qu[y]] && bid[qv[x]] == bid[qv[y]] && qk[x] < qk[y]; });
int u = 1, v = 1, ver = 0;
update(1);
for (int i = 1; i <= qcnt; ++i) {
int x = id[i];
if (u != qu[x]) work(u, qu[x]);
if (v != qv[x]) work(v, qv[x]);
update(lca(u, v));
update(lca(qu[x], qv[x]));
u = qu[x];
v = qv[x];
while (ver < qk[x]) ver1(++ver);
while (ver > qk[x]) ver2(ver--);
ans[x] = ret;
}
for (int i = 1; i <= qcnt; ++i) printf("%lld
", ans[i]);
return 0;
}
//} int main() { return cyl::main(); }
Children Trips
题意：给定一棵树n个点，边权为1或2。有m个询问，每次给出u，v，p。表示要从点u到点v，每天只能至多p的长度，且只能在节点处停留。对于每个询问，求至少需要几天。
主要方法：对于这种指定方向跳的题目，在序列上有分块的做法，在树上也可以用。可以发现每次的只询问一条路径。所以选择限制直径、限制个数、不限制大小的树分块。
1、对于(p>sqrt{n})的情况，可以证明暴力跳的话不会超过(O(sqrt{n}))次。
2、对于(p<sqrt{n})的情况，可以预处理每个点每种p的答案。然后每次一块一块跳，由于限制了个数，所以也是(O(sqrt{n}))的。
考虑一个询问u，v，p。令lca(u,v)=l。可以证明从u到l每天跳最多+从v到l每天跳最多=直接从u到v每天条最多=答案。需要注意的是，u到l最后一天剩下距离x，v到l最后一天剩下距离y，如果(x+y>=p)那么答案可以减少1。
#include <bits/stdc++.h>
using namespace std;
int n, w, fa[100005], d[100005], m, key[100005], p, fly[100005][680], stp[100005][680], lef[100005][680];
vector<pair<int, int> > G[100005];
int dfs1(int u, int dep) {
int siz = 1;
for (int i = 0; i < G[u].size(); ++i) {
int v = G[u][i].first;
if (v == fa[u])
continue;
d[v] = d[u] + G[u][i].second;
fa[v] = u;
siz += dfs1(v, dep + 1);
}
if (dep % w == 1 && (u == 1 || siz >= w)) {
key[u] = u;
siz = 0;
}
return siz;
}
void dfs2(int u) {
if (!key[u])
key[u] = key[fa[u]];
fly[u][0] = u;
for (int i = 1; i <= w + w; ++i) {
fly[u][i] = fly[u][i - 1];
if (fly[u][i] != key[u] && d[u] - d[fa[fly[u][i]]] <= i)
fly[u][i] = fa[fly[u][i]];
if (fly[u][i] == key[u]) {
stp[u][i] = 1;
lef[u][i] = i - (d[u] - d[key[u]]);
} else {
stp[u][i] = stp[fly[u][i]][i] + 1;
lef[u][i] = lef[fly[u][i]][i];
}
}
for (int i = 0; i < G[u].size(); ++i) {
int v = G[u][i].first;
if (v == fa[u])
continue;
dfs2(v);
}
}
int LCA(int u, int v) {
while (key[u] != key[v]) {
if (d[key[u]] < d[key[v]])
swap(u, v);
u = fa[key[u]];
}
while (u != v) {
if (d[u] < d[v])
swap(u, v);
u = fa[u];
}
return u;
}
int work(int u, int e, int &s) {
if (u == e)
return 0;
int LEF = 0;
if (p > 2 * w) {
while (key[u] != key[e]) {
if (d[u] - d[fa[key[u]]] <= LEF)
LEF -= d[u] - d[fa[key[u]]];
else {
++s;
LEF = p - d[fly[u][LEF]] + d[fa[key[u]]];
}
u = fa[key[u]];
}
} else {
while (key[u] != key[e]) {
if (d[u] - d[fa[key[u]]] <= LEF)
LEF -= d[u] - d[fa[key[u]]];
else {
u = fly[u][LEF];
s += stp[u][p];
LEF = lef[u][p];
if (d[key[u]] - d[fa[key[u]]] <= LEF)
LEF -= d[key[u]] - d[fa[key[u]]];
else {
++s;
LEF = p - d[key[u]] + d[fa[key[u]]];
}
}
u = fa[key[u]];
}
}
while (u != e) {
if (d[u] - d[fa[u]] <= LEF)
LEF -= d[u] - d[fa[u]];
else {
++s;
LEF = p - d[u] + d[fa[u]];
}
u = fa[u];
}
return LEF;
}
int main() {
scanf("%d", &n);
w = sqrt(n);
for (int i = 1; i < n; ++i) {
int u, v, w;
scanf("%d%d%d", &u, &v, &w);
G[u].push_back(make_pair(v, w));
G[v].push_back(make_pair(u, w));
}
dfs1(1, 1);
dfs2(1);
scanf("%d", &m);
while (m--) {
int u, v;
scanf("%d%d%d", &u, &v, &p);
int lca = LCA(u, v), s1 = 0, s2 = 0;
int l1 = work(u, lca, s1);
int l2 = work(v, lca, s2);
printf("%d
", s1 + s2 - (l1 + l2 >= p));
}
return 0;
}
```