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所以线段树分治我其实到今天才会

线段树分治板子题

• 线段树分治的时候注意叶子节点不要忘了撤销操作

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#include <bits/stdc++.h>
using namespace std;
#define INF 0x3f3f3f3f
#define N 100010
#define fir first
#define sec second
#define pb push_back
#define ll long long
//#define int long long

char buf[1<<21], *p1=buf, *p2=buf;
#define getchar() (p1==p2&&(p2=(p1=buf)+fread(buf, 1, 1<<21, stdin)), p1==p2?EOF:*p1++)
inline int read() {
	int ans=0, f=1; char c=getchar();
	while (!isdigit(c)) {if (c=='-') f=-f; c=getchar();}
	while (isdigit(c)) {ans=(ans<<3)+(ans<<1)+(c^48); c=getchar();}
	return ans*f;
}

int n, m;
int dsu[N];
ll siz[N], inv[N], ans=1;
const ll mod=1e9+7;
map<pair<int, int>, int> mp;
inline int find(int p) {return dsu[p]==p?p:find(dsu[p]);}
int tl[N<<2], tr[N<<2];
vector<int> del[N<<2];
vector<pair<int, int>> add[N<<2];
#define tl(p) tl[p]
#define tr(p) tr[p]
void build(int p, int l, int r) {
	tl(p)=l; tr(p)=r;
	if (l==r) return ;
	int mid=(l+r)>>1;
	build(p<<1, l, mid);
	build(p<<1|1, mid+1, r);
}
void upd(int p, int l, int r, pair<int, int> val) {
	if (l<=tl(p)&&r>=tr(p)) {add[p].pb(val); return ;}
	int mid=(tl(p)+tr(p))>>1;
	if (l<=mid) upd(p<<1, l, r, val);
	if (r>mid) upd(p<<1|1, l, r, val);
}
void query(int p) {
	for (auto it:add[p]) {
		int s=find(it.fir), t=find(it.sec);
		if (s==t) continue;
		if (siz[s]>siz[t]) swap(s, t);
		del[p].pb(s);
		ans=ans*inv[siz[s]]%mod*inv[siz[t]]%mod;
		siz[dsu[s]=t]+=siz[s];
		ans=ans*siz[t]%mod;
	}
	if (tl(p)==tr(p)) printf("%lld\n", ans);
	else query(p<<1), query(p<<1|1);
	while (del[p].size()) {
		auto it=del[p].back();
		ans=ans*inv[siz[find(it)]]%mod;
		siz[find(it)]-=siz[it];
		ans=ans*siz[find(it)]%mod*siz[it]%mod;
		dsu[it]=it;
		del[p].pop_back();
	}
}

signed main()
{
	freopen("b.in", "r", stdin);
	freopen("b.out", "w", stdout);
	
	n=read(); m=read();
	build(1, 1, m);
	inv[0]=inv[1]=1;
	for (int i=2; i<=n; ++i) inv[i]=(mod-mod/i)*inv[mod%i]%mod;
	for (int i=1; i<=n; ++i) siz[dsu[i]=i]=1;
	for (int i=1,u,v; i<=m; ++i) {
		if (read()&1) {
			u=read(); v=read();
			if (u>v) swap(u, v);
			mp[{u, v}]=i;
		}
		else {
			u=read(); v=read();
			if (u>v) swap(u, v);
			upd(1, mp[{u, v}], i-1, {u, v});
			mp.erase({u, v});
		}
	}
	for (auto it:mp) upd(1, it.sec, m, it.fir);
	query(1);
	
	return 0;
}