11.14 模拟赛小记

#include<bits/stdc++.h>
#define db double
using namespace std;
const int N=1e5+10;
db H;
int n;
struct node{int t,h;}a[N];
bool cmp(node x,node y){return x.t<y.t;}
priority_queue<db> q;
int flag;
int main(){
	scanf("%lf%d",&H,&n);
	for(int i=1;i<=n;i++){
		scanf("%d%d",&a[i].t,&a[i].h);
		if(!a[i].h) flag=1;
	}
	if(!flag){puts("-1");return 0;}
	sort(a+1,a+n+1,cmp);
	db ans=0;
	for(int i=1;i<=n;i++){
		db t=a[i].t-a[i-1].t;
		while(q.size()&&q.top()>=H) q.pop();
		while(q.size()&&H-q.top()<=t*1.0*q.size()){
			t-=(H-q.top())*1.0/q.size();
			H=q.top();
			if(H==0){
				ans=a[i].t-t;
				break;
			}
			q.pop();
		}
		if(t>0) H-=t*q.size();
		q.push(a[i].h);
	}
	if(ans){
		printf("%.6lf\n",ans);
		return 0;
	}
	ans=a[n].t;
	while(q.size()){
		ans+=(H-q.top())*1.0/q.size();
		H=q.top();
		q.pop();
	}
	printf("%.6lf",ans);
	return 0;
}