18D (贪心)

 题：http://codeforces.com/problemset/problem/18/D

对于每个顾客，若之前存在其要求的x，将其记录下来。然后将记录下来的x进行排序，取最大的,因为2^x>2^(x-1)+2^(x-2)+……

 

import java.math.*;
import java.util.*;

public class Main {
    static class node
    {
        int x,l,r;
    }
    static class cmp implements Comparator<node>
    {
        public int compare(node a,node b)
        {
            return a.x-b.x;
        }
    }
    static Boolean vis[]=new Boolean[5005];
    static BigInteger a[]=new BigInteger[2005];
    static node w[]=new node[5005];
    static int f[]=new int[2005];
    public static void main(String args[])
    {
        Scanner cin=new Scanner(System.in);
        int i;
        a[0]=BigInteger.valueOf(1);
        a[1]=BigInteger.valueOf(2);
        for(i=2;i<=2000;++i) a[i]=a[i-1].multiply(a[1]);
        while(cin.hasNextInt())
        {
            int n=cin.nextInt(),x,t=0;
            String s;
            Arrays.fill(f,0);
            Arrays.fill(vis, false);
            for(i=1;i<=n;++i)
            {
                s=cin.next();
                x=cin.nextInt();
                if(s.equals("win")==true) f[x]=i;
                else
                {
                    if(f[x]!=0)
                    {
                        w[t]=new node();
                        w[t].x=x;
                        w[t].l=f[x];
                        w[t++].r=i;
                    }
                }
            }
            Arrays.sort(w,0,t,new cmp());
            BigInteger ans=BigInteger.valueOf(0);
            for(i=t-1;i>=0;--i)
            {
                Boolean flag=true;
                for(int j=w[i].l;j<=w[i].r;++j)
                {
                    if(vis[j]==true){flag=false;break;}
                }
                if(flag==true)
                {
                    for(int j=w[i].l;j<=w[i].r;++j)
                        vis[j]=true;
                    ans=ans.add(a[w[i].x]);
                }
            }
            System.out.println(ans);
        }
        cin.close();
    }
}