Timus 1303

用动态规划超时了，悲剧，没想到可以用贪心O(n)就搞定了。

#include<iostream>

#include<cstdio>

#include<cstring>

#include<algorithm>

using namespace std;

struct node

{

    int x,y;

}vert[100010];

int res[100010];

int cmp(node a,node b)

{

    return a.x < b.x;

}

int work(int n,int m)

{

    int i,k=0,max=0,count=0,pre=0;

    if(n==0) return 0;

    for(i=0;i<n;i++)

    {

        if(vert[i].x<=pre)

        {

            if(max < vert[i].y)

            {

                max=vert[i].y; k=i; 

            }

        }

        else

        {

            if(vert[i].x>max) return 0;

            pre=max;

            res[count++]=k;

            if(pre>=m) return count;



            max=vert[i].y;

            k=i;

        }

    }

    if(max<m) return 0;

    res[count++]=k;

    return count;

}

int main()

{

    int i,n,s,t,count,r;

    while(scanf("%d",&n)!=EOF)

    {

        count=0;

        scanf("%d %d",&s,&t);

        while(s!=0 || t!=0)

        {

            if(!(t<=0 || s>=n))

            {

                vert[count].x=s; vert[count].y=t;

                count++;

            }

            scanf("%d %d",&s,&t);

        }

        sort(vert,vert+count,cmp);

        r=work(count,n);

        if(r)

        {

            printf("%d\n",r);

            for(i=0;i<r;i++)

                printf("%d %d\n",vert[res[i]].x,vert[res[i]].y);

        }

        else

        {

            printf("No solution\n");

        }



    }

    return 0;



}