https://www.luogu.com.cn/record/228613498

本帖禁水。

#include<bits/stdc++.h>
using namespace std;
typedef long long ll;
const int maxn=1e6+10;
int n,m,k,pos[maxn],cnt[maxn],vis[maxn],sta[maxn];
ll py[maxn],dp[maxn];
inline void check(ll mid){
	int pl=1,pr=1;
	py[0]=1ll*pos[0]*pos[0]-2*pos[0];
	for(int i=1;i<=n;i++){
		if(!vis[i]){
			dp[i]=dp[i-1];
			cnt[i]=cnt[i-1];
			continue;
		}
		while(pl<pr and (py[sta[pl+1]]-py[sta[pl]])<2ll*i*(pos[sta[pl+1]]-pos[sta[pl]])) pl++;
		dp[i]=py[sta[pl]]-2ll*i*pos[sta[pl]]+1ll*i*i+2*i+1+mid;
		cnt[i]=cnt[sta[pl]]+1;
		py[i]=dp[i]+1ll*pos[i]*pos[i]-2*pos[i]-1ll*max(0,i-pos[i]+1)*max(0,i-pos[i]+1);
		while(pl<pr and (__int128)(py[sta[pr]]-py[sta[pr-1]])*(pos[i]-pos[sta[pr]])>(__int128)(py[i]-py[sta[pr]])*(pos[sta[pr]]-pos[sta[pr-1]])) pr--;
		sta[++pr]=i;
	}
	return;
}
int main(){
	ios::sync_with_stdio(0);
	cin.tie(0); cout.tie(0);
	cin>>m>>n>>k;
	int ro,c;
	for(int i=0;i<=n;i++) pos[i]=1e9;
	for(int i=1;i<=m;i++){
		cin>>ro>>c;
		ro++,c++;
		if(ro>c) swap(ro,c);
		pos[c-1]=min(pos[c-1],ro);
		vis[c]=1;
	}
	for(int i=n;i>=1;i--) pos[i-1]=min(pos[i-1],pos[i]);
	ll l=0,r=1e12,mid,res=0;
	while(l<=r){
		mid=(l+r)>>1;
		check(mid);
		if(cnt[n]<=k) res=mid,r=mid-1;
		else l=mid+1;
	}
	check(res);
	cout<<(dp[n]-k*res)<<"\n";
	return 0;
}