Submission #823883

#	Time	Username	Problem	Language	Result	Execution time	Memory
823883		borisAngelov	XOR Sum (info1cup17_xorsum)	C++17	100 / 100	995 ms	25520 KiB

xorsum

#include <bits/stdc++.h>

using namespace std;

const int maxn = 1000005;

int n;
int a[maxn];
int b[maxn];

bool check(int bit)
{
    int result = 0;
    int cnt = 0;
    vector<int> rems;

    for (int i = 1; i <= n; ++i)
    {
        if ((a[i] & (1 << bit)) != 0)
        {
            ++cnt;
        }

        rems.push_back((a[i] % (1 << bit)));
    }

    result = (1LL * result + (1LL * cnt) * (1LL * (n - cnt))) % 2;

    sort(rems.begin(), rems.end());

    int r = n - 1;

    for (int l = 0; l < n; ++l)
    {
        if (l > r)
        {
            ++r;
        }

        while (r > l && rems[l] + rems[r - 1] >= (1 << bit))
        {
            --r;
        }

        if (rems[l] + rems[r] >= (1 << bit))
        {
            result = (result + n - r) % 2;
        }
    }

    int ptr1 = 1;
    int ptr2 = n - cnt + 1;

    for (int i = 1; i <= n; ++i)
    {
        if ((a[i] & (1 << bit)) != 0)
        {
            b[ptr2++] = a[i];
        }
        else
        {
            b[ptr1++] = a[i];
        }
    }

    for (int i = 1; i <= n; ++i)
    {
        a[i] = b[i];
    }

    return result;
}

void fastIO()
{
    ios_base::sync_with_stdio(0);
    cin.tie(0);
    cout.tie(0);
}

int main()
{
    fastIO();

    cin >> n;
    int max_val = 0;

    for (int i = 1; i <= n; ++i)
    {
        cin >> a[i];
        max_val = max(max_val, a[i]);
    }

    int ans = 0;

    int up_to = 0;
    int curr = 1;

    while (curr < max_val)
    {
        ++up_to;
        curr *= 2;
    }

    for (int i = 0; i <= up_to; ++i)
    {
        if (check(i) == true)
        {
            ans += (1 << i);
        }
    }

    cout << ans << endl;

    return 0;
}

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