LCS(最长公共子序列)

#include<bits/stdc++.h>
using namespace std;
#define ll long long
#define mp make_pair
#define pb push_back   //vector函数
#define popb pop_back  //vector函数
#define fi first
#define se second
const int N=1e5+10;
//const int M=;
//const int inf=0x3f3f3f3f;     //一般为int赋最大值,不用于memset中
//const ll INF=0x3ffffffffffff; //一般为ll赋最大值,不用于memset中
int T,n,a[N],b[N],c[N],pos[N],f[N];
inline int read()
{
    int x=0,f=1;char ch=getchar();
    while(ch<'0'||ch>'9'){if(ch=='-')f=-1;ch=getchar();}
    while(ch>='0'&&ch<='9'){x=(x<<1)+(x<<3)+(ch^48);ch=getchar();}
    return x*f;
}
int main()
{
//    freopen("","r",stdin);
//    freopen("","w",stdout);
    n=read();
    for(int i=1;i<=n;i++) a[i]=read(),pos[a[i]]=i;
    for(int i=1;i<=n;i++) b[i]=read(),c[i]=pos[b[i]]; 将b数组离散化成c数组
    int ans=0;
    for(int i=1;i<=n;i++)
    {
        int l=1,r=ans;
        if(!ans) { ans=1,f[1]=c[1];continue; }
        while(l+1<r)
        {
            int mid=(l+r)/2;
            if(f[mid]<c[i]) l=mid;
            else r=mid;
        }
        int len;
        if(f[r]<c[i]) len=r;
        else if(f[l]<c[i]) len=l;
        else len=0;
        if(!f[len+1]) f[len+1]=c[i];
        else f[len+1]=min(f[len+1],c[i]);
        ans=max(ans,len+1);
    }
    printf("%d\n",ans);
    return 0;
}