SGU 119 Beautiful People

#include <cstdio>
#include <cstring>
#include <algorithm>
using namespace std;
#define maxx 100050
struct node
{
    int a,b,id;
}g[maxx];
int root[maxx];
int id[maxx];
int len;
void output(int x)
{
    if(x==-1)return;
    output(root[x]);
    printf("%d ",g[x].id);
}
int cmp (node x,node y)
{
    if(x.a!=y.a)
    return x.a<y.a;
    return x.b>y.b;
}
int main()
{
    int n;
    scanf("%d",&n);
    for(int i=1;i<=n;i++)
    {
        scanf("%d%d",&g[i].a,&g[i].b);
        g[i].id=i;
    }
    sort(g+1,g+n+1,cmp);
    int len=1;
    int l,r;
    id[0]=1;
    memset(root,-1,sizeof(root));
    for(int i=2;i<=n;i++)
    {
        if(g[i].b>g[id[len-1]].b)
        {
            id[len++]=i;
            root[i]=id[len-2];
            continue;
        }
        l=0;
        r=len-1;
        while(l<r)
        {
            int mid=(l+r)>>1;
            if(g[i].b>g[id[mid]].b) l=mid+1;
            else  r=mid;
        }
        id[l]=i;
        if(l==0)  root[l]=-1;
        else  root[i]=id[l-1];
    }
    printf("%d\n",len);
    output(id[len-1]);
    puts("");
}

SGU 119 Beautiful People