两道贪心题

一、
P1809 渡河问题
二、
P1325 雷达覆盖

#include<iostream>#include<cstdio>#include<cstring>#include<algorithm>#define LL long longusing namespace std;const int N=100009;int n,a[N];LL ans;int main(){    scanf("%d",&n);    for(int i=1;i<=n;i++) scanf("%d",&a[i]);    sort(a+1,a+n+1);    int m=n;    while(m)    {        if(m==1) ans+=a[1];        if(m==2) ans+=a[2];        if(m==3) ans+=a[1]+a[2]+a[3];        if(m<=3) break;        LL s=a[2]+a[1]+a[m]+a[2];//1,2过去,1回来，m,m-1过去，2回来         LL ss=a[m]+a[1]+a[m-1]+a[1];//1,m过去，1回来，1,m-1过去，1回来         ans+=min(ss,s);        m-=2;    }    printf("%lld",ans);    return 0;} 

#include<iostream>#include<cstdio>#include<cstring>#include<algorithm>#include<cmath> #define LL long longusing namespace std;int n,d,ans;struct H{    int l,r;}q[100009]; bool vis[100009];bool cmp(H a,H b){    return a.r<b.r;}int main(){    scanf("%d%d",&n,&d);    for(int i=1;i<=n;i++)    {        int x,y;        scanf("%d%d",&x,&y);        if(d<abs(y)) {cout<<-1;return 0;}         int len=sqrt(d*d-y*y);        q[i].l=x-len,q[i].r=x+len;    }     sort(q+1,q+n+1,cmp);    for(int i=1;i<=n;i++)    {        if(!vis[i])        {            ans++;            for(int j=i+1;j<=n;j++)              if(q[j].l<=q[i].r&&q[j].r>=q[i].l)                vis[j]=1;        }    }    printf("%d\n",ans);    return 0;}