longest Increasing subsequence

http: // .  lightoj.com/article_show.php?article=1000&language=english&type=pdf

#include<bits/stdc++.h>
using namespace std;

#define si(n) scanf("%d",&n)
#define MAX 100005
#define INF 0x3f3f3f3f

int arr[MAX],t[MAX],l[MAX];

int main()
{
    //freopen("input.txt","r",stdin);
    int i,j,n;
    si(n);
    for(i=0;i<n;i++)si(arr[i]);

    memset(t,INF,sizeof(t));
    int mx_len=0;

    for(i=0;i<n;i++){
        int lo=0,hi=mx_len+1;
        while(hi-lo>1){
            int mid=(hi+lo)/2;
            if(t[mid]>=arr[i])hi=mid;
            else lo=mid;
        }
        lo++;
        t[lo]=arr[i];
        l[i]=lo;
        mx_len=max(mx_len,lo);
    }

    printf("%d\n",mx_len);

    return 0;
}