#include <bits/stdc++.h>
#pragma GCC optimize("Ofast")
#pragma GCC optimize("unroll-loops")
using namespace std;
const int N = 1e6 + 11;
int a[N], b0[N], b0n, b1[N], b1n;
int main(){
int n; cin >> n;
for(int i = 0; i < n; i++){
cin >> a[i];
}
int ans = 0;
for(int s = 0; s <= 29; s++){
int c = 0;
b0n = b1n = 0;
for(int j = 0; j < n; j++){
if(a[i] & (1 << s)) b0[b0n++] = a[i] % (1 << s);
else b1[b1n++] = a[i] % (1 << s);
}
sort(b0, b0 + b0n); sort(b1, b1 + b1n);
int r = b0n;
for(int l = 0; l < b0n; l++){
r = max(r, l + 1);
while(r - 1 > l && b0[l] + b0[r - 1] >= (1 << s)) r--;
c += b0n - r;
}
r = b1n;
for(int l = 0; l < b1n; l++){
r = max(r, l + 1);
while(r - 1 > l && b1[l] + b1[r - 1] >= (1 << s)) r--;
c += b1n - r;
}
r = b1n;
for(int l = 0; l < b0n; l++){
r = max(r, l + 1);
while(r - 1 > l && b0[l] + b1[r - 1] >= (1 << s)) r--;
c += b1n - r;
}
ans ^= (1 << s) * (c % 2);
}
cout << ans << endl;
}
Compilation message
xorsum.cpp: In function 'int main()':
xorsum.cpp:20:9: error: 'i' was not declared in this scope
20 | if(a[i] & (1 << s)) b0[b0n++] = a[i] % (1 << s);
| ^
