CF1208F Bits And Pieces

Posted 2022-08-30 skip1978

#include<bits/stdc++.h>
const int maxn = 1 << 21;
int c[maxn],a[maxn],n;
inline void ins(int x,int b)
    if(c[x] >= 2) return ;
    if(b == -1) return void(++c[x]);
    ins(x,b-1);
    if(x >> b & 1) ins(x ^ 1 << b,b-1);

inline int qry(int x)
    int ret = 0,p = 0;
    for(int i=20;~i;--i)
        if(x >> i & 1) ret |= 1 << i;
        else if(c[p | 1 << i] >= 2)
            ret |= 1 << i,p |= 1 << i;
    return ret;

int main()
    std::ios::sync_with_stdio(false),std::cin.tie(0);
    std::cin >> n;
    for(int i=1;i<=n;++i) std::cin >> a[i];
    int ans = 0;
    for(int i=n;i>=1;--i)
        if(i <= n - 2) ans = std::max(qry(a[i]),ans);
        ins(a[i],20);
    
    std::cout << ans << '\n';