贪心——poj 3171 Cleaning Shifts

区间覆盖最小代价

由于N<=10000

排序后想到N*N的遍历

不断更新add[i](表示到i最小代价)里的值，使之最小

View Code

#include<stdio.h>
#include<iostream>
#include<algorithm>
using namespace std;

const int maxint=999999999;
struct data
{
    int ll,rr,c;
}s[10009];

int add[10009];

int cmp(data a,data b)
{
    if(a.ll==b.ll)
        return a.rr<b.rr;
    else
        return a.ll<b.ll;
}

int main()
{
    int n,begin,end;
    while(scanf("%d%d%d",&n,&begin,&end)!=EOF)
    {
        int i,j;
        for(i=1;i<=n;i++)
        {
            scanf("%d%d%d",&s[i].ll,&s[i].rr,&s[i].c);
            add[i]=maxint;
            s[i].rr++;
            
        }
        sort(&s[1],&s[n+1],cmp);
        
        if(s[1].ll>begin)
        {
            printf("-1\n");continue;
        }

        int mmax=s[1].rr;
        for(i=1;i<n;i++)
        {
            if(mmax>=s[i+1].ll)
            {
                mmax=max(mmax,s[i+1].rr);
            }
            else
            {
                break;
            }
        }
        if(mmax-1<end)
        {
            printf("-1\n");continue;
        }

        add[1]=s[1].c;
        for(i=1;i<=n;i++)
        {
            if(s[i].ll<=begin)
                add[i]=s[i].c;
            for(j=i+1;j<=n;j++)
            {
                if(s[i].ll==s[j].ll)continue;
                if(s[i].rr>=s[j].rr)continue;
                if(s[i].rr<s[j].ll)break;

                add[j]=min(add[j],add[i]+s[j].c);
            }
        }

        int mmin=maxint;
        for(i=1;i<=n;i++)
        {
            if(s[i].rr-1>=end)
                mmin=min(mmin,add[i]);
        }

        printf("%d\n",mmin);
    }
}