1333: [NOIP2004]合并果子

#include<iostream>
#include<algorithm>
using namespace std;
const int N(30005);
long long a[N],b[N];
int main()
{
    int n,i,j,k,m,c;
    long long x,ans(0);
    cin>>n;
    fill(a,a+N,0x7fffffff);
    fill(b,b+N,0x7fffffff);
    for(i=0;i<n;i++)
        cin>>a[i];
    sort(a,a+n);
    for(i=j=m=0,k=1;k<n;k++)
    {
        x=a[i]+a[i+1];
        c=1;
        if(a[i]+b[j]<x)
        {
            x=a[i]+b[j];
            c=2;
        }
        if(b[j]+b[j+1]<x)
        {
            x=b[j]+b[j+1];
            c=3;
        }
        switch(c)
        {
            case 1:
                b[m++]=x;
                i+=2;
                break;
            case 2:
                b[m++]=x;
                i++;
                j++;
                break;
            case 3:
                b[m++]=x;
                j+=2;
                break;
        }
        ans+=b[m-1];
    }
    cout<<ans;
    return 0;
}