Submission #485728

#	Time	Username	Problem	Language	Result	Execution time	Memory
485728		ak2006	XOR Sum (info1cup17_xorsum)	C++14	0 / 100	2 ms	332 KiB

xorsum

#include <bits/stdc++.h>
using namespace std;
using ll = long long;
using vb = vector<bool>;
using vvb = vector<vb>;
using vi = vector<int>;
using vvi = vector<vi>;
using vl = vector<ll>;
using vvl = vector<vl>;
using vc = vector<char>;
using vvc = vector<vc>;
using vs = vector<string>;
const ll mod = 1e9 + 7,inf = 1e18;
#define pb push_back
#define fast ios_base::sync_with_stdio(0);cin.tie(0);cout.tie(0);
void setIO()
{
    fast;
    #ifndef ONLINE_JUDGE
    freopen("input.txt","r",stdin);
    freopen("output.txt","w",stdout);
    #endif
}
int n;
bool valid(int l,int r)
{
    return l >= 0 and r <= n - 1 and l <= r;
}
int main()
{
    setIO();
    cin>>n;
    
    vi v(n);
    for (int i = 0;i<n;i++)
        cin>>v[i];

    ll ans = 0;

    for (int b = 1;b<=30;b++){
        vi bits(n);
        for (int i = 0;i<n;i++){
            int x = v[i];
            int num = 0;
            int cnt = 0;
            vi digs;
            while (x > 0 and cnt < b){
                digs.pb(x%2);
                x /= 2;
                cnt++;
            }
            reverse(digs.begin(),digs.end());
            for (int i = 0;i<digs.size();i++){
                int pos = (digs.size() - i - 1);
                num += digs[i] * (1<<pos);
            }
            bits[i] = num;

        }
        
        sort(bits.begin(),bits.end());
        
        //sum of the 2 "b" bit (and hence (b - 1)th position)
        //numbers should be
        //in the range
        //[1<<(b - 1), (1<<b) - 1]
        //OR
        //[(1<<b) + (1<<(b - 1)), (1<<(b + 1)) - 2]

        ll cnt = 0;

        for (int i = 0;i<n;i++){
            int s1 = lower_bound(
                bits.begin() + i,bits.end(), (1<<(b - 1)) - bits[i])
             - bits.begin();
            
            int e1 = -1;

            int l = i,r = n - 1;
            while (l <= r){
                int mid = (l + r)/2;
                if (bits[i] + bits[mid] <= (1<<b) - 1){
                    e1 = mid;
                    l = mid + 1;
                }
                else r = mid - 1;
            }
            
            int s2 = lower_bound(
                bits.begin() + i,bits.end(),-bits[i] + (1<<b) + 
                (1<<(b - 1))) - bits.begin();
            
            int e2 = -1;
            l = i,r = n - 1;
            while (l <= r){
                int mid = (l + r)/2;
                if (bits[i] + bits[mid] <= (1<<(b + 1)) - 2){
                    e2 = mid;
                    l = mid + 1;
                }
                else r = mid - 1;
            }

            ll num = 0;
            if (valid(s1,e1) and valid(s2,e2)){
                assert(s1 < s2);
                if (e1 < s2)
                    num = (e1 - s1 + 1) + (e2 - s2 + 1);
                else
                    num = (e2 - s1 + 1);
            }
            else if (valid(s1,e1))
                num = e1 - s1 + 1;
            else if (valid(s2,e2))
                num = e2 - s2 + 1;
            
            assert(num >= 0);
            cnt += num;
        }
        if (cnt%2 == 1)ans += (1<<(b - 1));
    }
    cout<<ans<<endl;
    return 0;
}

Compilation message (stderr)

xorsum.cpp: In function 'int main()':
xorsum.cpp:53:29: warning: comparison of integer expressions of different signedness: 'int' and 'std::vector<int>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   53 |             for (int i = 0;i<digs.size();i++){
      |                            ~^~~~~~~~~~~~
xorsum.cpp: In function 'void setIO()':
xorsum.cpp:20:12: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)' declared with attribute 'warn_unused_result' [-Wunused-result]
   20 |     freopen("input.txt","r",stdin);
      |     ~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~
xorsum.cpp:21:12: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)' declared with attribute 'warn_unused_result' [-Wunused-result]
   21 |     freopen("output.txt","w",stdout);
      |     ~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~

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