POJ1716 Integer Intervals

 1 /**/
 2 #include<iostream>
 3 #include<cstdio>
 4 #include<cmath>
 5 #include<cstring>
 6 #include<algorithm>
 7 using namespace std;
 8 const int mxn=50000;
 9 struct area{
10     int l,r;
11 }a[mxn];
12 int n;
13 int ans,f,s;
14 int cmp(area a,area b){
15     if(a.r!=b.r)return a.r<b.r;
16     return a.l<b.l;
17 }
18 int main(){
19     scanf("%d",&n);
20     int i,j;
21     for(i=1;i<=n;i++)scanf("%d%d",&a[i].l,&a[i].r);
22     sort(a+1,a+n+1,cmp);
23     ans=2;f=a[1].r;s=a[1].r-1;
24     for(i=2;i<=n;i++){
25         if(f<a[i].l){
26             ans+=2;
27             f=a[i].r;
28             s=a[i].r-1;
29             continue;
30         }
31         if(s<a[i].l){
32             ans++;
33             if(f>a[i].r-1)    s=a[i].r-1;
34             else s=f;
35             f=a[i].r;
36             continue;
37         }
38         if(f>a[i].r)f=a[i].r;
39     }
40     printf("%d\n",ans);
41     return 0;
42 }