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;

}