Submission #496873

#	Time	Username	Problem	Language	Result	Execution time	Memory
496873		Ziel	XOR Sum (info1cup17_xorsum)	C++17	7 / 100	1693 ms	131076 KiB

xorsum

/**
 * LES GREATEABLES BRO TEAM
**/

#include <bits/stdc++.h>
#include <ext/pb_ds/assoc_container.hpp>

using namespace std;
using namespace __gnu_pbds;

template<class T>
using ordered_set = tree<T, null_type, less<T>, rb_tree_tag, tree_order_statistics_node_update>;
using ll = long long;
#define sz(x) (int)x.size()
const bool FLAG = false;
void setIO(const string &f = "");

void solve() {
    int n;
    cin >> n;
    vector<int> a(n);
    int mx = 0, res = 0;
    for (int &x: a) {
    	cin >> x;
    	mx = max(mx, x);
    }

    if (n * n <= 4e8) {
    	for (int i = 0; i < n; i++) {
    		for (int j = i; j < n; j++) {
    			res ^= (a[i] + a[j]);
    		}
    	}
    } else if (mx * mx <= 4e8) {
    	set<pair<int, int>> s;
    	ordered_set<int> occ[mx + 1];
    	for (int i = 0; i < n; i++) {
    		s.insert({i, a[i]});
    		occ[a[i]].insert(i);
    	}
    	vector<int> v(mx + mx + 2);
    	for (int a = 1; a <= mx; a++) {
    		for (int b = 1; b <= mx; b++) {
    			for (int pos: occ[a]) {
    				int k = sz(occ[b]) - occ[b].order_of_key(pos);
					v[a + b] += k;
    			}
    		}
    	}
    	for (int i = 1; i <= mx + mx; i++)
    		res ^= (v[i] % 2) * i;
    }

	cout << res;
}

signed main() {
    setIO();
    
    int tt = 1;
    if (FLAG) {
    	cin >> tt;
    }
    while (tt--) {
    	solve();
    }
    
    return 0;
}

void setIO(const string &f) {
    ios_base::sync_with_stdio(false);
    cin.tie(nullptr);
    if (fopen((f + ".in").c_str(), "r")) {
        freopen((f + ".in").c_str(), "r", stdin);
        freopen((f + ".out").c_str(), "w", stdout);
    }
}

Compilation message (stderr)

xorsum.cpp: In function 'void setIO(const string&)':
xorsum.cpp:75:16: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)' declared with attribute 'warn_unused_result' [-Wunused-result]
   75 |         freopen((f + ".in").c_str(), "r", stdin);
      |         ~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
xorsum.cpp:76:16: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)' declared with attribute 'warn_unused_result' [-Wunused-result]
   76 |         freopen((f + ".out").c_str(), "w", stdout);
      |         ~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

• Subtask 1: 7 / 7
• Subtask 2: 0 / 11
• Subtask 3: 0 / 21
• Subtask 4: 0 / 38
• Subtask 5: 0 / 23