BZOJ 1537 Aut- The Bus

#include<iostream>
#include<cstdio>
#include<cstring>
#include<algorithm>
#define maxn 100050
using namespace std;
long long n,m,k,hash[maxn],tot=0,t[maxn],f[maxn];
struct pnt
{
    long long x,y,w;
}p[maxn];
bool cmp(pnt x,pnt y)
{
    if (x.x!=y.x) return x.x<y.x;
    return x.y<y.y;
}
long long find(long long x)
{
    return lower_bound(hash+1,hash+tot+1,x)-hash;
}
long long lowbit(long long x) {return (x&(-x));}
long long ask(long long x)
{
    long long ret=0;
    for (long long i=x;i>=1;i-=lowbit(i))
        ret=max(ret,t[i]);
    return ret;
}
void modify(long long x,long long val)
{
    for (long long i=x;i<=tot;i+=lowbit(i))
        t[i]=max(t[i],val);
}
int main()
{
    scanf("%lld%lld%lld",&n,&m,&k);
    for (long long i=1;i<=k;i++)
    {
        scanf("%lld%lld%lld",&p[i].x,&p[i].y,&p[i].w);
        hash[++tot]=p[i].y;
    }    
    k++;p[k].x=n;p[k].y=m;p[k].w=0;hash[++tot]=m;
    sort(p+1,p+k+1,cmp);sort(hash+1,hash+tot+1);tot=unique(hash+1,hash+tot+1)-hash-1;
    for (long long i=1;i<=k;i++)
    {
        long long ret=find(p[i].y);
        f[i]=ask(ret)+p[i].w;modify(ret,f[i]);
    }
    printf("%lld\n",f[k]);
    return 0;
}