CF515 DIV3 B heaters 区间覆盖问题

版权声明：https://github.com/godspeedcurry 欢迎加好友哦 https://blog.csdn.net/qq_38677814/article/details/83035189

感觉对这个算法理解不是很透彻，就是个贪心嘛，代码调了半天调不出来
贪心：左端点合法的约束下，一直选能更新到最大右区间的线段

#include <bits/stdc++.h>
using namespace std;
#define ll long long
const ll MOD = 1e9+7;
#define pb push_back
#define mp(a,b) make_pair(a,b)
int n,m;
vector<pair<int,int> > G;
int main(){
	ios::sync_with_stdio(0);
	int n,r;
	cin>>n>>r;
	for(int i=1;i<=n;++i){
		int data;
		cin>>data;
		int L=max(1,i-r+1);
		int R=min(n,i+r-1);
		if(data) G.pb(mp(L,R));
	}
	sort(G.begin(),G.end());
	int now=1;
	int ans=0;
	int temp=0;
	int index=0;
	int len=G.size();
	bool ok=true;
	while(now<=n){
		temp=0;
		while(index<len&&G[index].first<=now){
			temp=max(temp,G[index].second);
			++index;
		}
		if(!temp){
			ok=0;
			break;
		}
		now=temp+1;
		ans++;
	}
	if(!ok){
		printf("-1\n");
	}
	else printf("%d\n",ans);
	return 0;
}