2018 蓝桥杯 C++ A组

 9. 倍数问题

#include<bits/stdc++.h>
using namespace std;
typedef long long ll;

const int maxn=1e5;

ll nn,k,vis[maxn],tmp[maxn],num[maxn];
vector<ll>vc;

ll dfs(ll n)
{
	if(n>=3)
    {
		ll t=tmp[0]+tmp[1]+tmp[2];
		if(t%k==0)
			vc.push_back(t);
	}
	else
		for(int i=0;i<nn;i++)
			if(vis[i]==0)
				tmp[n]=num[i],vis[i]=1,dfs(n+1),vis[i]=0;
}
int main()
{
	scanf("%lld%lld",&nn,&k);
	memset(vis,0,sizeof(vis));
	memset(num,0,sizeof(num));
	memset(tmp,0,sizeof(tmp));
	for(int i=0;i<nn;i++)
		scanf("%lld",&num[i]);
	dfs(0);
	ll ans=0;
    for(int i=0;i<vc.size();i++)
    	ans=max(ans,vc[i]);
	printf("%lld\n",ans);
	return 0;
}

10. 付账问题

#include<bits/stdc++.h>
using namespace std;
const int maxn = 5e5+5;
int a[maxn],n,s;

int main()
{
	scanf("%d %d",&n,&s);
	for(int i = 0;i<n;i++)
		scanf("%d",&a[i]);
	double avg=(double)s/n,ls=double(s),nowavg=avg,dis=0;
	sort(a,a+n);
	for(int i=0;i<n;i++)
    {
        if(a[i]<nowavg)
        {
            dis+=(a[i]-avg)*(a[i]-avg);
            ls-=a[i];
            nowavg=ls/(n-i-1);
        }
        else
        {
            dis+=(nowavg-avg)*(nowavg-avg);
            ls-=nowavg;
        }
    }
    printf("%.4lf\n",sqrt(dis/n));
	return 0;
}