Submission #442593

#	Time	Username	Problem	Language	Result	Execution time	Memory
442593		Theo830	Xor Sort (eJOI20_xorsort)	C++17	100 / 100	9 ms	1484 KiB

xorsort

#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
const ll INF = 1e9+7;
const ll MOD = 998244353;
typedef pair<ll,ll> ii;
#define iii pair<ii,ll>
#define f(i,a,b) for(ll i = a;i < b;i++)
#define pb push_back
#define vll vector<ll>
#define F first
#define S second
#define all(x) (x).begin(), (x).end()
///I hope I will get uprating and don't make mistakes
///I will never stop programming
///sqrt(-1) Love C++
///Please don't hack me
///@TheofanisOrfanou Theo830
///Think different approaches (bs,dp,greedy,graphs,shortest paths,mst)
///Stay Calm
///Look for special cases
///Beware of overflow and array bounds
///Think the problem backwards
///Training
int main(void){
    ios_base::sync_with_stdio(0);
    cin.tie(0);
    ll n,s;
    cin>>n>>s;
    ll arr[n];
    f(i,0,n){
        cin>>arr[i];
    }
    vector<ii>ans;
    if(s == 1 || n <= 200){
        ll pre = 0;
        f(j,0,n){
            ll maxi = -1;
            ll pos = 0;
            f(i,0,n-j){
                maxi = max(maxi,arr[i] ^ pre);
                if(maxi == (arr[i] ^ pre)){
                    pos = i;
                }
            }
            pre = maxi;
            f(i,0,n-j-1){
                ans.pb(ii(i+1,i+2));
                arr[i] ^= arr[i+1];
            }
            f(i,pos,n-j-1){
                ans.pb(ii(i+2,i+1));
                arr[i+1] ^= arr[i];
            }
            for(ll i = pos-1;i >= 1;i--){
                ans.pb(ii(i,i+1));
                arr[i-1] ^= arr[i];
            }
        }
        for(ll i = n-2;i >= 0;i--){
            ans.pb(ii(i+1,i+2));
            arr[i] ^= arr[i+1];
        }
    }
    else{
        for(ll j = 19;j >= 0;j--){
            bool ivra = 0;
            f(i,0,n){
                if(arr[i] & (1LL<<j)){
                    ivra = 1;
                }
                else if(ivra){
                    ans.pb(ii(i+1,i));
                    arr[i] ^= arr[i-1];
                }
            }
            f(i,0,n-1){
                if(arr[i] & (1LL<<j)){
                    ans.pb(ii(i+1,i+2));
                    arr[i] ^= arr[i+1];
                }
            }
            n -= ivra;
        }
    }
    cout<<ans.size()<<"\n";
    for(auto x:ans){
        cout<<x.F<<" "<<x.S<<"\n";
    }
}
/*
5 1
3 2 8 4 1

5 2
4 4 2 0 1
*/

• Subtask 1: 25 / 25
• Subtask 2: 35 / 35
• Subtask 3: 40 / 40