Codeforces Round#499 (Div. 2)

比赛传送门

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A. Stages

直接贪心尽量取小字母就好了

#include<cstdio>

int n,k,num[30];
char s[55];
int main(){
	scanf("%d%d%s",&n,&k,s);
	for (int i=0;i<n;i++) num[s[i]-'a'+1]++;
	int lst=-1,ans=0;
	while (k){
		int i;bool suc=0;
		for (i=lst+2;i<=26;i++)
		 if (num[i]) {suc=1;break;}
		if (!suc) break;
		ans+=i;lst=i;k--;
	}
	if (k) return puts("-1"),0;
	printf("%d",ans);
	return 0;
}

B. Planning The Expedition

二分天数，看总共是否够n个人吃

#include<cstdio>

const int maxn=105;
int n,m,num[maxn];
bool check(int day){
	int tot=0;
	for (int i=1;i<=100;i++) tot+=num[i]/day;
	return tot>=n;
}
int main(){
	scanf("%d%d",&n,&m);
	for (int i=1,x;i<=m;i++) scanf("%d",&x),num[x]++;
	int l=1,r=10000,ans=0;
	while (l<=r){
		int mid=l+r>>1;
		if (check(mid)) ans=mid,l=mid+1;else r=mid-1;
	}
	printf("%d",ans);
	return 0;
}

C. Fly

显然油带得多不会影响飞行，所以二分油量即可

此题卡精度差评……

#include<cstdio>

const int maxn=1005;
const long double eps=1e-9;
int n,m,a[maxn],b[maxn];
bool check(long double fuel){
	for (int i=2;i<=n+1;i++){
		double del=(fuel+m)/a[i-1];
		if (del-fuel>=eps) return 0;
		fuel-=del;
		del=(fuel+m)/b[i];
		if (del-fuel>=eps) return 0;
		fuel-=del;
	}
	return 1;
}
int main(){
	scanf("%d%d",&n,&m);
	long double ans=-1,l=0,r=1e9;
	for (int i=1;i<=n;i++) scanf("%d",&a[i]),l+=(double)m/a[i];
	for (int i=1;i<=n;i++) scanf("%d",&b[i]),l+=(double)m/b[i];
	a[n+1]=a[1],b[n+1]=b[1];
	while (r-l>=eps){
		long double mid=(l+r)/2;
		if (check(mid)) ans=mid,r=mid;else l=mid;
	}
	if (ans<0) return puts("-1"),0;
	printf("%.10lf",(double)ans);
	return 0;
}

D. Rocket

看这里

E. Border

看这里

F. Mars rover

看这里