[APIO/CTSC 2007] 数据备份(反悔贪心)

Posted 2021-10-24 thusloop

数据备份
题意：在数组中选择k个数使得和最小，且不能相邻。

//#pragma GCC optimize(2)
//#pragma GCC optimize(3,"Ofast","inline")
#include<bits/stdc++.h>
#define int long long
#define fi first
#define se second
#define pii pair<int,int>
#define ios ios::sync_with_stdio(false);cin.tie(0);cout.tie(0);
using namespace std;
const int inf=2e18+100;
const int maxn=2e5+100;
int a[maxn],l[maxn],r[maxn];
bool vis[maxn];
priority_queue<pii,vector<pii>,greater<pii>>q;
signed main()
{
	IOS
	int n,k;
	cin>>n>>k;
	for(int i=1; i<=n; i++)
	{
		cin>>a[i];
	}
	for(int i=1; i<n; i++)
	{
		a[i]=a[i+1]-a[i];
		l[i]=i-1;
		r[i]=i+1;
		q.push({a[i],i});
	}
	n--;
	a[0]=a[n+1]=inf;
	int ans=0,cnt=0;
	while(!q.empty())
	{
		auto now=q.top();
		q.pop();
		if(vis[now.se])continue;
		vis[l[now.se]]=vis[r[now.se]]=1;
		ans+=now.fi;
		cnt++;
		if(cnt==k)break;
		a[now.se]=a[l[now.se]]+a[r[now.se]]-a[now.se];//左右信息放入中间的点
		q.push({a[now.se],now.se});
		//修改左右相邻信息
		l[now.se]=l[l[now.se]];
		r[now.se]=r[r[now.se]];
		r[l[now.se]]=now.se;
		l[r[now.se]]=now.se;
	}
	cout<<ans<<"\\n";
}