/* Enjoying CP as always!*/
#include <bits/stdc++.h>
using namespace std;
#define int long long

signed main() {
    ios_base::sync_with_stdio(false);
    cin.tie(NULL);
    int t;
    cin>>t;
    while(t--) {
        //Take input
        int n;
        cin>>n;
        int a[n];
        for(int i=0;i<n;i++) {
            cin>>a[i];
        }
        //initialize answer..
        int ans=0;
        for(int i=0;i+1<n;i++) {
            ans+=(!((a[i]^a[i+1])&1));
            /*XOR the two numbers and check 0th bit in the resultant, if it is 1
            then, numbers are of different parity, otherwise both are of same parity*/
        }
        cout<<ans<<"\n";
    }
    return 0;
}

def main():
    T = int(input())
    while T > 0:
        T = T - 1
        n = int(input())
        a = [int(x) for x in input().split()]
        ans = 0
 
        for i in range(1, n):
            ans += 1 - ((a[i] + a[i - 1]) & 1)
 
        print(ans)
 
 
if __name__ == '__main__':
    main()

• Good problem:
• Average problem:
• Bad problem:
• Did not solve:

#include<bits/stdc++.h>
using namespace std;
#define int long long
signed main()
{
    const int N = 1e5 + 5;
    const int mod = 1e9 + 7;
    vector<int> fact(N);
    fact[0] = 1;
    for(int i = 1; i < N; i++)
    {
        fact[i] = fact[i - 1] * i;
        fact[i] %= mod;
    }
    int t;
    cin >> t;
    while(t--)
    {
        int n;
        cin >> n;
        int ans = n * (n - 1);
        ans %= mod;
        ans = (ans * fact[n]) % mod;
        cout << ans << endl;
    }
    return 0;
}

t = int(input())
for _ in range(t):
    n = int(input())
    nf = 1
    mod = int(1e9 + 7)
    for i in range(n):
        nf = nf * (i + 1)
        nf %= mod
    ans = n * (n - 1) * nf
    ans %= mod
    print(ans)

• Good problem:
• Average problem:
• Bad problem:
• Did not solve:

#include <bits/stdc++.h>
#define all(v) v.begin(), v.end()
#define var(x, y, z) cout << x << " " << y << " " << z << endl;
#define ll long long int
#define pii pair<ll, ll>
#define pb push_back
#define ff first
#define ss second
#define FASTIO                \
    ios ::sync_with_stdio(0); \
    cin.tie(0);               \
    cout.tie(0);

using namespace std;

const ll inf = 1e17;
const ll MAXM = 1e5;
vector<ll> factors[MAXM + 5];

void init()
{
    for (ll i = 1; i <= MAXM; i++)
    {
        for (ll j = i; j <= MAXM; j += i)
        {
            factors[j].pb(i);
        }
    }
}

void solve()
{
    ll n, m;
    cin >> n >> m;
    vector<pii> vec;
    for (ll i = 0; i < n; i++)
    {
        ll value;
        cin >> value;
        vec.pb({value, i});
    }
    sort(all(vec));
    vector<ll> frequency(m + 5, 0);
    ll curr_count = 0;
    ll j = 0;
    ll global_ans = inf;
    for (ll i = 0; i < n; i++)
    {
        for (auto x : factors[vec[i].ff])
        {
            if (x > m)
                break;
            if (!frequency[x]++)
            {
                curr_count++;
            }
        }
        while (curr_count == m)
        {
            ll curr_ans = vec[i].ff - vec[j].ff;
            if (curr_ans < global_ans)
            {
                global_ans = curr_ans;
            }
            for (auto x : factors[vec[j].ff])
            {
                if (x > m)
                    break;
                if (--frequency[x] == 0)
                {
                    curr_count--;
                }
            }
            j++;
        }
    }
    cout << (global_ans >= inf ? -1 : global_ans) << "\n";
}

int main()
{
    FASTIO
    init();
    ll t;
    cin >> t;
    while (t--)
    {
        solve();
    }
    return 0;
}

• Good problem:
• Average problem:
• Bad problem:
• Did not solve:

#include <bits/stdc++.h>
using namespace std;
 
#define MOD 1000000007
 
long long power(long long a, int b)
{
    long long ans = 1;
    while (b)
    {
        if (b & 1)
        {
            ans *= a;
            ans %= MOD;
        }
        a *= a;
        a %= MOD;
        b >>= 1;
    }
    return ans;
}
 
int DFS(int v, vector<int> edges[], int p, int dep, int ped[])
{
    int mdep = dep;
    for (auto it : edges[v])
        if (it != p)
            mdep = max(DFS(it, edges, v, dep + 1, ped), mdep);
    ped[v] = mdep - dep + 1;
    return mdep;
}
 
int main()
{
    ios_base::sync_with_stdio(false);
    cin.tie(NULL);
    int T, i, j, n, u, v;
    cin >> T;
    while (T--)
    {
        cin >> n;
        vector<int> edges[n];
        for (i = 0; i < n - 1; i++)
        {
            cin >> u >> v;
            u--, v--;
 
            edges[u].push_back(v);
            edges[v].push_back(u);
        }
 
        int ped[n];
        DFS(0, edges, 0, 0, ped);
 
        long long p = power(2, n - 1), ans = 0;
        for (i = 0; i < n; i++)
        {
            ans += p * ped[i] % MOD;
            ans %= MOD;
        }
        cout << ans << "\n";
    }
}

• Good problem:
• Average problem:
• Bad problem:
• Did not solve:

#include <bits/stdc++.h>
using namespace std;
 
// Using Kosa Raju, we guarantee the topmost element (indicated by root) of stack is from the root SCC
 
void DFS(int v, bool visited[], int &root, vector<int> edges[])
{
    visited[v] = true;
    for (auto it : edges[v])
        if (!visited[it])
            DFS(it, visited, root, edges);
    root = v;
}
 
int cnt(int v, bool visited[], vector<int> edges[])
{
    int ans = 1;
    visited[v] = true;
    for (auto it : edges[v])
        if (!visited[it])
            ans += cnt(it, visited, edges);
    return ans;
}
 
int main()
{
    ios_base::sync_with_stdio(false);
    cin.tie(NULL);
    int T;
    cin >> T;
    while (T--)
    {
        int i, j, n, m, u, v, w;
        cin >> n >> m;
        vector<pair<int, int>> og_edges[n];
        for (i = 0; i < m; i++)
        {
            cin >> u >> v >> w;
            u--, v--;
 
            og_edges[u].push_back({v, w});
        }
 
        int l = -1, r = 1e9 + 1, mid;
        while (r - l > 1)
        {
            mid = l + (r - l) / 2;
 
            vector<int> edges[n];
            for (i = 0; i < n; i++)
            {
                for (auto it : og_edges[i])
                {
                    edges[i].push_back(it.first);
                    if (it.second <= mid)
                        edges[it.first].push_back(i);
                }
            }
 
            bool visited[n] = {};
            int root;
            for (i = 0; i < n; i++)
            {
                if (!visited[i])
                    DFS(i, visited, root, edges);
            }
 
            memset(visited, false, sizeof(visited));
 
            if (cnt(root, visited, edges) == n)
                r = mid;
            else
                l = mid;
        }
 
        if (r == 1e9 + 1)
            r = -1;
        cout << r << '\n';
    }
    return 0;
}

• Good problem:
• Average problem:
• Bad problem:
• Did not solve:

#include <bits/stdc++.h>
 
using namespace std;
 
struct Trie{
	struct Trie *child[2]={0};
};
typedef struct Trie trie;
 
void insert(trie *dic, int x)
{
	trie *temp = dic;
	for(int i=30;i>=0;i--) 
	{
		int curr = x>>i&1;
		if(temp->child[curr])
			temp = temp->child[curr];
		else
		{
			temp->child[curr] = new trie;
			temp = temp->child[curr];
		}
	}
}
 
int find_greatest(trie *dic, int x) {
	int res = 0;
	trie *temp = dic;
	for(int i=30;i>=0;i--) {
		int curr = x>>i&1;
		if(temp->child[curr^1]) {
			res ^= 1<<i;
			temp = temp->child[curr^1];
		}
		else {
			temp = temp->child[curr];
		}
	}
	return res;	
}
 
int main() {
	int test_cases;
	cin >> test_cases;
	while(test_cases--)
	{
		int n;
		cin>>n;
		int a[n+1];
		for(int i=1;i<=n;i++) {
			cin>>a[i];
		}
 
		trie *t[n+2];
		int prexor[n+1];
		prexor[0] = 0;
		for(int i=1;i<=n;i++) {
			t[i] = new trie;
			insert(t[i], prexor[i-1]);
			prexor[i] = prexor[i-1]^a[i];
		}
		t[n+1] = new trie;
		insert(t[n+1], prexor[n]);
		
		pair<int,int> asc[n+1];
		for(int i=1;i<=n;i++) {
			asc[i] = make_pair(a[i],i);
		}
		sort(asc+1,asc+n+1);
		
		int left[n+1], right[n+1];
		stack<int> s;
		for(int i=1;i<=n;i++) {
			while(!s.empty() && a[i]>=a[s.top()])
				s.pop();
			if(s.empty())
				left[i] = 0;
			else
				left[i] = s.top();
			s.push(i);
		}
		while(!s.empty()) 
			s.pop();
		for(int i=n;i>0;i--) {
			while(!s.empty() && a[i]>a[s.top()])
				s.pop();
			if(s.empty())
				right[i] = n+1;
			else
				right[i] = s.top();
			s.push(i);
		}
		
		int ans = 0;
		for(int i=1;i<=n;i++) {
			int x = asc[i].second;
			int r = right[x]-1;
			int l = left[x]+1;
			if(x-l < r-x) {
				for(int j=l-1;j<x;j++) {
					ans = max(ans, find_greatest(t[x+1], prexor[j]^a[x]));
				}
				t[l] = t[x+1];
				for(int j=l-1;j<x;j++) {
					insert(t[l], prexor[j]);
				}
			}
			else {
				for(int j=x;j<=r;j++) {
					ans = max(ans, find_greatest(t[l], prexor[j]^a[x]));
				}
				for(int j=x;j<=r;j++) {
					insert(t[l], prexor[j]);
				}
			}
		}
		cout<<ans << endl;
	}
}

• Good problem:
• Average problem:
• Bad problem:
• Did not solve: