Submission #1091671

#	Time	Username	Problem	Language	Result	Execution time	Memory
1091671		efishel	Xor Sort (eJOI20_xorsort)	C++17	25 / 100	87 ms	18528 KiB

xorsort

#include <bits/stdc++.h>
using namespace std;
using ll = long long;
using vll = vector <ll>;
using ii = pair <ll, ll>;
using vii = vector <ii>;

const ll MAXN = 1E3+16;
ll th[MAXN];
vii ans;
void fop (vll &ve, ll i, ll j) {
    ans.push_back({ i, j });
    ve[i] ^= ve[j];
    th[i] ^= th[j];
}
void fswap (vll &ve, ll i) { // swap the indices (i, i+1)
    fop(ve, i, i+1);
    fop(ve, i+1, i);
    fop(ve, i, i+1);
}

void fsolve (vll &ve, ll l, ll r, ll bit) {
    if (bit == -1 || l > r) return;
    for (ll i = l; i <= r; i++) th[i] = ve[i]>>bit&1;
    for (ll i = l; i <= r; i++) {
        for (ll j = l; j < r; j++) {
            if (ve[j] > ve[j+1]) {
                fswap(ve, j);
            }
        }
    }
    // ll il = l, ir = r;
    // while (il < ir) {
    //     while (il < ir && th[il] == 0) il++;
    //     while (il < ir && th[ir] == 1) ir--;
    //     if (il >= ir) break;
    //     fswap(ve, il, ir);
    //     il++; ir--;
    // }
    for (ll i = l; i <= r; i++) th[i] = ve[i]>>bit&1;
    // assert(is_sorted(th+l, th+r+1));
    ll mid = r;
    while (th[mid] == 1) mid--;
    fsolve(ve, l, mid, bit-1);
    fsolve(ve, mid+1, r, bit-1);
}

int main () {
    cin.tie(nullptr) -> sync_with_stdio(false);
    ll n, s;
    cin >> n >> s;
    vll ve(n);
    for (ll &i : ve) cin >> i;
    fsolve(ve, 0, n-1, 19);
    cout << ans.size() << '\n';
    for (auto [i, j] : ans) cout << i+1 << ' ' << j+1 << '\n';
    // for (ll i : ve) cerr << i << ' ';
    return 0;
}


/*

3, 2
3, 1
2, 1
2, 3
1, 3

2, 2

 */

• Subtask 1: 25 / 25
• Subtask 2: 0 / 35
• Subtask 3: 0 / 40