Submission #389254

#	Time	Username	Problem	Language	Result	Execution time	Memory
389254		abc864197532	XOR Sum (info1cup17_xorsum)	C++17	56 / 100	1699 ms	10864 KiB

xorsum

#include <bits/stdc++.h>
using namespace std;
#define lli long long int
#define pb push_back
#define eb emplace_back
#define mp make_pair
#define test(x) cout << #x << ' ' << x << endl
#define printv(x) { \
    for (auto a : x) cout << a << ' '; \
    cout << endl; \
}
#define pii pair<int, int>
#define pll pair<lli, lli>
#define X first
#define Y second
#define all(x) x.begin(), x.end()
#define rall(x) x.rbegin(), x.rend()
const int N = 200000, abc = 864197532;

int main () {
    ios::sync_with_stdio(false);
    cin.tie(0);
    int n;
    cin >> n;
    vector <int> a(n);
    for (int i = 0; i < n; ++i) cin >> a[i];
    int ans = 0, mx = *max_element(all(a));
    for (int k = __lg(mx) + 1; ~k; --k) {
        for (int i = 0; i < n; ++i) if (a[i] >= (1 << k + 1)) a[i] -= (1 << k + 1);
        sort(all(a));
        int cnt = 0;
        for (int i = 0; i < n; ++i) {
            int r = lower_bound(all(a), (1 << k + 1) - a[i]) - a.begin() - i;
            int l = lower_bound(all(a), (1 << k) - a[i]) - a.begin() - i;
            r = max(r, 0), l = max(l, 0);
            cnt ^= (r - l) & 1;
            r = n - i;
            l = lower_bound(all(a), 3 * (1 << k) - a[i]) - a.begin() - i;
            l = max(l, 0);
            cnt ^= (r - l) & 1;
        }
        /*
         * check k bit
         * mod 2^{k + 1}
         * 1 3
         * count pair 2^k <= a + b < 2^{k + 1}
         * 3 * 2^k - a > b
         */
        if (cnt) ans |= 1 << k;
    }
    cout << ans << endl;
}

Compilation message (stderr)

xorsum.cpp: In function 'int main()':
xorsum.cpp:29:57: warning: suggest parentheses around '+' inside '<<' [-Wparentheses]
   29 |         for (int i = 0; i < n; ++i) if (a[i] >= (1 << k + 1)) a[i] -= (1 << k + 1);
      |                                                       ~~^~~
xorsum.cpp:29:79: warning: suggest parentheses around '+' inside '<<' [-Wparentheses]
   29 |         for (int i = 0; i < n; ++i) if (a[i] >= (1 << k + 1)) a[i] -= (1 << k + 1);
      |                                                                             ~~^~~
xorsum.cpp:33:49: warning: suggest parentheses around '+' inside '<<' [-Wparentheses]
   33 |             int r = lower_bound(all(a), (1 << k + 1) - a[i]) - a.begin() - i;
      |                                               ~~^~~

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