BZOJ3126: [Usaco2013 Open]Photo

n<=200000个点，m<=100000个区间，每个区间有且仅有一个点，求最多几个点，无解-1。

http://www.cnblogs.com/Chorolop/p/7570191.html

WA了两次：看成最少几个点；判无解是<0而不一定=-inf。

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

 int n,m;
 #define maxn 200011
 int l[maxn],r[maxn],f[maxn];
 int que[maxn],head,tail;
 int x,y;const int inf=0x3f3f3f3f;
 int main()
 {
     scanf("%d%d",&n,&m);
     for (int i=;i<=n+;i++) r[i]=i-;
     memset(l,,sizeof(l));
     for (int i=;i<=m;i++)
     {
         scanf("%d%d",&x,&y);
         r[y]=min(r[y],x-);
         l[y+]=max(l[y+],x);
     }
     for (int i=n;i>=;i--) r[i]=min(r[i+],r[i]);
     for (int i=;i<=n+;i++) l[i]=max(l[i-],l[i]);
     que[head=(tail=)-]=;f[]=;
     for (int i=;i<=n+;i++)
     {
         for (int j=r[i-]+;j<=r[i];j++)
         {
             while (head<tail && f[que[tail-]]<=f[j]) tail--;
             que[tail++]=j;
         }
         while (head<tail && que[head]<l[i]) head++;
         if (head<tail) f[i]=f[que[head]]+;
         else f[i]=-inf;
     }
     if (f[n+]<) puts("-1");
     else printf("%d\n",f[n+]-);
     return ;
 }