#include<bits/stdc++.h> using namespace std; #define fi first #define se second #define pb push_back #define eb emplace_back #define vi vector<int> #define pi pair<int,int> #define sz(v) (int)(v).size() #define all(v) (v).begin(), (v).end() #define compact(v) (v).erase(unique(all(v)), (v).end()) template<class T> using upq = priority_queue<T, vector<T>, greater<T>>; template<class T> int lwrbound(const vector<T>& a, const T& b, const int s = 0){return int(lower_bound(s + all(a), b) - a.begin());} template<class T> int uprbound(const vector<T>& a, const T& b, const int s = 0){return int(upper_bound(s + all(a), b) - a.begin());} #define FOR(i, a, b) for(int i = (a); i <= (b); i++) #define ROF(i, a, b) for(int i = (a); i >= (b); i--) #define sumof(x) accumulate(all(x), 0ll) #define dbg(x) "[" << #x " = " << (x) << "]" #define el "\n" using ll = long long; using ld = long double; template<class T> bool ckmx(T& a, const T b){return (a < b ? a = b, true : false);} template<class T> bool ckmn(T& a, const T b){return (a > b ? a = b, true : false);} const int lg = 29; /* brute: + fix a number x and bit B + get prefix sum in range [tL, tR] */ void Main() { int N; cin >> N; vi a(N + 1), o, z, v; FOR(i, 1, N){ cin >> a[i]; ((a[i] & 1) ? o.eb(i) : z.eb(i)); } v.insert(v.end(), all(z)); v.insert(v.end(), all(o)); int ans = 0; FOR(b, 0, lg + 1){ vector<pi> range; range.eb(pi((1ll << b), (1ll << b + 1) - 1)); range.eb(pi((1ll << b + 1) | (1ll << b), (1ll << b + 2) - 1)); auto f = [&](int x) -> int{ return (a[x] & ((1 << b + 1) - 1)); }; int cnt = 0; FOR(_, 0, 1){ int L, R; L = R = sz(v) - 1; FOR(i, 0, sz(v) - 1){ while(R >= i && f(v[R]) + f(v[i]) > range[_].se) --R; while(L >= i && f(v[L]) + f(v[i]) >= range[_].fi) --L; if(R >= i){ cnt ^= ((R - max(i - 1, L)) & 1); } } } ans = ans | (cnt << b); o.clear(), z.clear(); for(int i : v){ (((a[i] >> (b + 1)) & 1) ? o.eb(i) : z.eb(i)); } v.clear(); v.insert(v.end(), all(z)); v.insert(v.end(), all(o)); } cout << ans << el; } int32_t main() { ios_base::sync_with_stdio(0); cin.tie(0); cout.tie(0); #define name "InvMOD" if(fopen(name".INP", "r")){ freopen(name".INP", "r", stdin); freopen(name".OUT", "w", stdout); } int t = 1; while(t--) Main(); return 0; }

xorsum.cpp: In function 'int32_t main()':
xorsum.cpp:94:16: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)' declared with attribute 'warn_unused_result' [-Wunused-result]
   94 |         freopen(name".INP", "r", stdin);
      |         ~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~
xorsum.cpp:95:16: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)' declared with attribute 'warn_unused_result' [-Wunused-result]
   95 |         freopen(name".OUT", "w", stdout);
      |         ~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~