# https://www.codechef.com/problems/XORED - HELP

``````#include <bits/stdc++.h>
using namespace std;
#define int     int64_t
#define IOS     ios::sync_with_stdio(0); cin.tie(0);

signed main() {
IOS;
int t; cin >> t;
const int M = 32;
int even = 4e5, odd = 4e5+1, zero = 0;
int even_two = 400000, odd_two = 400002;
int inf = 5e5+1;
while(t--) {
int n, x; cin >> n >> x;
cout << n << " " << x << "\n";
if(n == 1) {
cout << x << "\n";
} else if(n == 2) {
cout << 0 << " " << x << "\n";
} else {
set<int> ans;
int till = 0;
for(int i=1;i<=n-1;i++) {
// ans.insert(i);
till = till ^ i;
}
// n - 1 elements filled till here [1, 2, 3, ... n - 1]
int last = x ^ till;
// last ^ till = x; last = x ^ till;
// if last belongs to [1, 2, 3, ... n - 1]
if((last > 0) && (last < n)) {
auto it = ans.find(last);
if(last == 1) {
// don't want 1 in the array as [2 ^ 3 ^ ... ^ n - 1] = X
// erase 1 and 2
ans.erase(it);
// till = till ^ 1;
// till = till ^ 2;
// add three unique elements such that
ans.insert(even_two);
ans.insert(odd_two);
ans.insert(zero);
// till = till ^ even_two;
// till = till ^ odd_two;
// till = till ^ zero;
} else {
// don't want some number which is greater than one
ans.erase(it);
ans.erase(ans.begin());
// till = till ^ last;
// till = till ^ 1;
ans.insert(even);
ans.insert(odd);
ans.insert(zero);
// till = till ^ even;
// till = till ^ odd;
// till = till ^ zero;
}
} else {

ans.insert(last);
till = till ^ last;

}

// int i = 0;
// cout << "SIZE: " << ans.size() << "\n";
// for(auto num : ans) {
//     cout << i + 1 << " " << num << "\n";
//     i += 1;
// }
// till = 0;
// for(auto num : ans) {
//     till = till ^ num;
// }
cout << "XOR: " << till << "\n";

assert(ans.size() == n);
assert(till == x);

// for(auto num : ans) {
//     cout << num << " ";
// }
// cout << "\n";
}
}
}
``````

This code passes the first subtask but fails on every test case of the second subtask. I tried to debug it trying various test cases but it works on all of them. Can someone please point out why it is not working?

This code is giving SIGTSTP error. FIrstly, edit this code. It does not match to your last submission (which works fine).

``````#include <bits/stdc++.h>
using namespace std;
#define int     int64_t
#define IOS     ios::sync_with_stdio(0); cin.tie(0);

signed main() {
IOS;
int t; cin >> t;
const int M = 32;
int even = 4e5, odd = 4e5+1, zero = 0;
int even_two = 400000, odd_two = 400002;
while(t--) {
int n, x; cin >> n >> x;

if(n == 1) {
cout << x << "\n";
} else if(n == 2) {
cout << 0 << " " << x << "\n";
} else {
set<int> ans;
// ans[0] = even, ans[1] = odd;
int till = 0;
for(int i=1;i<=n-1;i++) {
ans.insert(i);
till = till ^ i;
}
// n - 1 elements filled till here [1, 2, 3, ... n - 1]
int last = x ^ till;
// last ^ till = x; last = x ^ till;
// if last belongs to [1, 2, 3, ... n - 1]
if((last > 0) && (last < n)) {
auto it = ans.find(last);
if(it == ans.begin()) {
// don't want 1 in the array as [2 ^ 3 ^ ... ^ n - 1] = X
// erase 1 and 2
ans.erase(it);
ans.erase(2);
// add three unique elements such that
ans.insert(even_two);
ans.insert(odd_two);
ans.insert(zero);
} else {
// don't want some number except one
ans.erase(it);
ans.erase(ans.begin());
ans.insert(even);
ans.insert(odd);
ans.insert(zero);
}
} else {
ans.insert(last);
}

int i = 0;
// cout << "SIZE: " << ans.size() << "\n";
// for(auto num : ans) {
//     cout << i + 1 << " " << num << "\n";
//     i += 1;
// }
till = 0;
for(auto num : ans) {
till = till ^ num;
}
// cout << "XOR: " << till << "\n";
// assert(ans.size() == n);
// assert(till == x);

for(auto num : ans) {
cout << num << " ";
}
cout << "\n";
}
}
}
``````

This is the edited code.