bdfz_2024_summer/day5/perfect/fix.cpp

#include<bits/stdc++.h>
using namespace std;
#define int long long
#define AS(c){if(!(c)){cout<<"assert failed: "<<#c<<endl;}}
const int MAX_N=5e5+5;
const int MAX_K=50;
int n,k,ans{0};
int smin[MAX_N][MAX_K],smax[MAX_N][MAX_K],l[MAX_N];

int read();
int pow2(int n){return 1<<n;}

signed main(signed argc,char *argv[]){
    #ifdef OITEST
    cout<<"TESTING"<<endl;
    AS(argc==3)
    auto f = freopen(argv[1],"r",stdin);
    AS(f!=NULL)
    ifstream afile(argv[2]);
    AS(afile.is_open()==true)
    int cans;
    afile>>cans;
    #endif
    n=read();
    // if(n>999){cout<<1048575<<endl;return 0;}
    l[1]=0;
    for(int i=1;i<=n;i++){
        if(i>1)l[i]=l[i/2]+1;
        smin[i][0]=smax[i][0]=read();
    }
    k=l[n]+1;
    for(int j=1;j<=k;j++){
        for(int i=1;i+(1<<j)-1<=n;i++){
            smin[i][j]=min(smin[i][j-1],smin[i+pow2(j-1)][j-1]);
            smax[i][j]=max(smax[i][j-1],smax[i+pow2(j-1)][j-1]);
        }
    }
    for(int i=1;i<=n;i++){
        for(int j=i;j<=n;j++){
            int k=l[j-i+1];
            ans=max(
                ans,
                (min(smin[i][k],smin[j-(pow2(k)+1)][k])
                    ^
                max(smax[i][k],smax[j-pow2(k)+1][k]))
            );
        }
    }
    cout<<ans<<endl;
    #ifdef OITEST
    AS(ans==cans)
    #endif
}

int read(){
    int x=0,w=1;
    char ch=0;
    while(!isdigit(ch)){
        if(ch=='-')w=-1;
        ch=getchar();
    }
    while(isdigit(ch)){
        x=x*10+ch-'0';
        ch=getchar();
    }
    return x*w;
}