csu 1538: Shopping（贪心）

#include<iostream>
#include<cstdio>
#include<cstring>
#include<cmath>
#include<stdlib.h>
#include<queue>
#include<algorithm>
#include<vector>
#include<ctype.h>
#define LL __int64
using namespace std;
const double EPS=1e-9;
const int MAXN=1000+10;
int vis[2000];
int gcd(int a,int b)
{
    return b?gcd(b,a%b):a;
}
int lcm(int a,int b)
{
    return a/gcd(a,b)*b;
}
typedef struct good
{
    int c;
    int d;
};
int main()
{
    int n,m;
    int i,j,k;
    int fl[MAXN],fr[MAXN];
    good p[MAXN];
 
    while(scanf("%d%d",&n,&m)!=EOF)
    {
        memset(vis,0,sizeof(vis));
        int exit=n+1,enter=0,start=0;
       for( i=1;i<=n;i++)
        {
            fl[i]=fr[i]=i;
        }
       for( i=1;i<=m;i++)
        {
            scanf("%d %d",&p[i].c,&p[i].d);
            vis[p[i].c]=1;
            vis[p[i].d]=1;
            fl[p[i].d]=p[i].c;
            fr[p[i].c]=p[i].d;
        }
        int flag=0;
        int ans=0;
        int  L=0,R=0;
        int last=0;
        for(i=1;i<=n+1;i++)
        {
            if(vis[i]==0)
            continue;
            if(flag==0)
            {
                flag++;
                ans+=(i-last);
                //printf(" %d  %d///\n",i,ans);
                L=i;
                R=fr[i];
            }
            else if(R<fl[i])
            {
                ans+=(R-L)*3;
                ans+=(i-R);
                //flag--;
                L=fl[i];
                R=fr[i];
                last=i;
                //printf("%d %d\n",i,ans);
            }
            else if(fl[i]<R&&R<fr[i])
            {
                R=fr[i];
            }
        }
        //printf("%d\n",ans);
        ans+=(n+1-R);
        //printf("%d\n",ans);
        ans+=(R-L)*3;
        printf("%d\n",ans);
    }
 
 
 
    return 0;
}