#include <bits/stdc++.h>
using namespace std;
#define ll long long
#define fast                       \
 ios_base::sync_with_stdio(0);      \
 cin.tie(0);                         \
 cout.tie(0);
 
int main(){
    fast;
    ll t;
    cin>>t;
    while(t--){
        int n,m;
        cin>>n>>m;
        cout<<((n+1)/2)*((m+1)/2)<<"\n";
    }
}

First let's assign a number to each sector from 1 to n in clockwise order.

#include <bits/stdc++.h>
using namespace std;
#define ll long long
#define fast                       \
 ios_base::sync_with_stdio(0);      \
 cin.tie(0);                         \
 cout.tie(0);
 
int main(){
    fast;
    ll t;
    cin>>t;
    while(t--){
        ll n;
        cin>>n;
        if(n%2==0){
            if((n/2)%2==1) cout<<"-1\n";
            else{
                ll x=(n/2);
                cout<<(x*(x+1))/2-(n/4)<<"\n";
            }
        }
        else{
            ll x=(n-1)/2;
            cout<<(x*(x+1))/2<<"\n";
        }
    }
}

#include<bits/stdc++.h>
#define pi 3.14159265358979323846
#define eb emplace_back
#define ll long long
#define w(t) while(t--)
#define F first
#define S second
#define pii pair<int,int>
#define pll pair<ll,ll>
#define iofast ios::sync_with_stdio(0);cin.tie(0);
using namespace std;
//give sin(),cos() radian, and asin(),acos() gives you radian
vector<int> v[1000010];
bool ch[1000010];
ll cnt1,cnt0;
void DFS(int po,bool c){
	if(!c) cnt0++;
	else cnt1++;
	ch[po]=1;
	for(auto i:v[po]){
		if(!ch[i]){
			DFS(i,!c);
		}
	}
	return;
}
void solve(){
	int n,a,b;
	cnt1=0;
	cnt0=0;
	cin>>n;
	for(int i=1;i<=n;i++){
		v[i].clear();
		ch[i]=0;
	}
	for(int i=1;i<n;i++){
		cin>>a>>b;
		v[a].eb(b);
		v[b].eb(a);
	}
	DFS(1,0);
	cout<<(((cnt1-1)*cnt1)/2)+(((cnt0-1)*cnt0)/2)<<'\n';
	return;
}
int main(){
	iofast
	int t;
	cin>>t;
	w(t) solve();
	return 0;
}

#include <bits/stdc++.h>
using namespace std;
#define ll long long
#define fast                       \
 ios_base::sync_with_stdio(0);      \
 cin.tie(0);                         \
 cout.tie(0);
 
int main(){
    fast;
    ll t;
    cin>>t;
    while(t--){
        ll n,k;
        cin>>n>>k;
        if(k<n || k>(n*(n+1))/2) cout<<"-1\n";
        else{
            if(k==n){
                for(ll i=1;i<n;i++) cout<<i<<" ";
                cout<<0<<"\n";
            }
            else if(k==(n*(n+1))/2){
                for(ll i=0;i<n;i++) cout<<i<<" ";
                cout<<"\n";
            }
            else{
                k-=n;
                vector<ll> ans(n);
                ll val=0,ind=0,ind1=0;
                for(ll i=0;i<n;i++) ans[i]=i;
                for(ll i=n-1;i>0;i--){
                    if(k>i) k-=i;
                    else{
                        swap(ans[i-1],ans[0]);
                        val=k;
                        ind=i;
                        break;
                    }
                }
                for(ll i=0;i<n;i++){
                    if(ans[i]==val){
                        ind1=i;
                        break;
                    }
                }
                swap(ans[ind],ans[ind1]);
                for(auto i:ans) cout<<i<<" ";
                cout<<"\n";
            }
        }
    }
}

Reimagine the integers in $$$a$$$ as binary integers. Since XOR operation is done before any addition, this means that we can count the contribution of each bit separately, because XOR operation can be done by doing the XOR operation for each bit, and addition can also be done in a similar way.

Let $$$s_k$$$ be the sum of costs from all $$$2^{n-1}$$$ possible expressions if we only consider the $$$k$$$-th bit from each integer as the elements. Then, the sum of costs is $$$\sum_{i=0}^{28} s_i \cdot 2^i$$$.

Let's try to count $$$s_0$$$. We will use dynamic programming to solve this. Let $$$dp_i$$$ be the sum of costs from all $$$2^{i-1}$$$ possible expressions if we only consider the $$$0$$$-th bit from each integer as the elements, and we only consider the first $$$i$$$ elements. Let the $$$0$$$-th bit of $$$a_i$$$ be $$$b_i$$$. Then, $$$dp_0 = 0$$$ and $$$dp_i = \sum_{x=0}^{i-1} (dp_x + (b_{x+1} \oplus b_{x+2} \oplus \dots \oplus b_i))$$$. Although doing this naively would result in $$$O(n^3)$$$ transition, we can optimize this to $$$O(n)$$$ using prefix sum.

Let $$$pdp_i = \sum_{x=0}^{i} dp_x$$$ and $$$pb_i = b_1 \oplus b_2 \oplus \dots \oplus b_i$$$. Then, $$$dp_i = pdp_{i-1} + \sum_{x=0}^{i-1} (pb_x \oplus pb_i)$$$. Notice that the second expression is still $$$O(n)$$$. So, to count it in $$$O(1)$$$, we just have to store two extra variables $$$c_{i,0}$$$ and $$$c_{i,1}$$$, where $$$c_{i,k}$$$ is the number of integers $$$x$$$ such that $$$1 \leq x \leq i$$$ and $$$pb_x = k$$$. If $$$pb_i = 0$$$, the second expression is equal to $$$c_{i,1}$$$. Otherwise, the second expression is equal to $$$c_{i,0}$$$.

Other values of $$$s_i$$$ can be counted in a similar way.

Time complexity: $$$O(n \log a_i)$$$

#include <bits/stdc++.h>
using namespace std;
#define ll long long
#define fast                       \
 ios_base::sync_with_stdio(0);      \
 cin.tie(0);                         \
 cout.tie(0);
 
ll mod=998244353;
const ll N=5e5+10;
vector<ll> po;

int main(){
    fast;
    po.resize(N);
    po[0]=1;
    for(ll i=1;i<N;i++) po[i]=(2*po[i-1])%mod;
    ll t;
    cin>>t;
    while(t--){
        ll n;
        cin>>n;
        vector<ll> a(n);
        for(ll i=0;i<n;i++) cin>>a[i];
        vector<ll> dp(n);
        vector<vector<ll>> v(n,vector<ll>(30));
        vector<ll> val(30,0);
        for(ll i=0;i<n;i++){
            for(ll j=0;j<30;j++){
                v[i][j]=val[j];
                if((a[i]&(1<<j))>0) val[j]=1-val[j];
            }
        }
        vector<vector<ll>> dp1(30,vector<ll>(2));
        ll ans=0;
        for(ll i=0;i<n;i++){
            dp[i]=ans;
            for(ll j=0;j<30;j++){
                dp1[j][v[i][j]]=(dp1[j][v[i][j]]+((1<<j)*(po[max((ll)0,i-1)]))%mod)%mod;
            }
            for(ll j=0;j<30;j++){
                if((a[i]&(1<<j))>0) dp[i]=(dp[i]+dp1[j][v[i][j]])%mod;
                else dp[i]=(dp[i]+dp1[j][1-v[i][j]])%mod;
            }
            ans=(ans+dp[i])%mod;
        }
        cout<<dp[n-1]<<"\n";
    }
}

#include <bits/stdc++.h>
using namespace std;
#define ll long long
#define fast                       \
 ios_base::sync_with_stdio(0);      \
 cin.tie(0);                         \
 cout.tie(0);

ll mod=1e9+7;
 
long long power(long long a,long long b){
  long long x=1,y=a;
  while(b>0){
    if(b&1ll){
      x=(x*y)%mod;
    }
    y=(y*y)%mod;
    b>>=1;
  }
  return x%mod;
}
 
long long modular_inverse(long long n){
  return power(n,mod-2);
}
 
#define MAXN 2000005
 
long long factorial[MAXN];
long long invfact[MAXN];
 
void cfact(){
  long long i;
  factorial[0]=1;
  factorial[1]=1;
  for(i=2;i<MAXN;i++){
    factorial[i]=factorial[i-1]*i;
    factorial[i]%=mod;
  }
  invfact[MAXN-1]=modular_inverse(factorial[MAXN-1]);
  for(i=MAXN-2;i>=0;i--){
    invfact[i]=invfact[i+1]*(i+1);
    invfact[i]%=mod;
  }
}
 
long long calcnCr(long long n,long long k){
  if(k<0 || n<k){return 0;}
  return (factorial[n]*((invfact[k]*invfact[n-k])%mod))%mod;
}

int main(){
    fast;
    cfact();
    ll t;
    cin>>t;
    while(t--){
        ll n;
        cin>>n;
        string s1,s2;
        cin>>s1>>s2;
        ll cnt11=count(s1.begin(),s1.end(),'1');
        ll cnt20=count(s2.begin(),s2.end(),'0');
        if(cnt11>0 && cnt20>0) cout<<"0\n";
        else if(cnt11==0 && cnt20>0) cout<<power((power(2,n)-1)%mod,n-cnt20)%mod<<"\n";
        else if(cnt11>0 && cnt20==0) cout<<power((power(2,n)-1)%mod,n-cnt11)%mod<<"\n";
        else{
            ll res=0;
            for(ll i=0;i<n;i++){
                if(i%2==0){
                    res=(res-((calcnCr(n,i+1))*power(2,n*n-(i+1)*n))%mod+mod)%mod;
                }
                else{
                    res=(res+((calcnCr(n,i+1))*power(2,n*n-(i+1)*n))%mod)%mod;
                }
            }
            cout<<(power(2,n*n)+2*res)%mod<<"\n";
        }
    }
}

WLOG, assume that $$$x \geq y$$$. We desire for Alice to win. Let us check the scenarios where this is possible:

Case 1: $$$(x \geq 2y)$$$: This means Alice has to subtract a multiple of $$$y$$$ from $$$x$$$. There are, say $$$k$$$ choices of subtracting $$$y, 2y, .., ky$$$. We have more than $$$1$$$ choices $$$(k>1)$$$. If $$$ky$$$ is winning, Alice chooses that. If it is losing, then since $$$k>1$$$, Alice can choose $$$(k-1)y$$$ and Bob will then be forces to subtract $$$y$$$ in the next move, essentially making Bob choose the losing $$$ky$$$ state. So Alice always wins.

Case 2: $$$(x<2y)$$$: This means there is only one possible move, which is to subtract $$$y$$$ from $$$x$$$. If the resulting pair of numbers $$$(y,x-y)$$$ is losing, Alice wins. Else she loses.

Now, for her to loose, like in case 1, $$$(y \geq 2(x-y))$$$ (we already know $$$y$$$ is larger than $$$(x-y)$$$ since $$$x<2y$$$). So for her to win, $$$y \leq 2(x-y)$$$, which means $$$x \geq \frac{3y}{2}$$$.

If $$$y<2(x-y)$$$, we again subtract and go to the next iteration. The new pair is $$$(x-y,2y-x)$$$. For it the winning conditions come out to be $$$x \geq \frac{5y}{3}$$$.

If we keep doing the iterations, we observe that in the $$$n^{th}$$$ step the condition comes out to be $$$x \geq \frac{F(n+1)}{F(n)}$$$ where $$$F(n)$$$ is the $$$n^{th}$$$ Fibonacci number $$$(F(1)=1, F(2)=2)$$$. So, to get the exact bound, we take its limit as $$$n$$$ approaches infinity, and get $$$\lim_{n \to \infty} \frac{F(n+1)}{F(n)} = \frac{1+\sqrt{5}}{2} = \phi$$$. So Alice wins iff $$$(x> \phi y)$$$ (equality dropped since both $$$x$$$ and $$$y$$$ are integers).

So our problem becomes counting the number of $$$(l,r)$$$ such that $$$r> \phi l$$$. Since our numbers $$$\leq 10^9$$$, we can take an appropriate approximation of $$$\phi$$$, (say $$$\frac{p}{q}$$$).

Now our problem boils down to calculating $$$\sum_{x=L'}^{R} \lfloor \frac{xq}{p} \rfloor$$$ (here $$$L'$$$ is the first index such that $$$\lfloor \frac{L'q}{p} \rfloor \geq L $$$).

This is a standard problem and can be calculated in $$$O(log(max(p,q))$$$ complexity. Here is reference a blog with exact details about solving this: https://www.cnblogs.com/apjifengc/p/17492207.html

#include <bits/stdc++.h>
using namespace std;

typedef long long int ll;
typedef long double ld;

const ll P = 1e18;
const ld phi=1.61803398874989;
const ll a=1134903170, b=0, c=1836311903;

struct Node {
    ll x, y, sumx, sumy;
    Node() : x(0), y(0), sumx(0), sumy(0) {}
    Node operator*(Node b) {
        Node a = *this, c;
        c.x = (a.x + b.x) % P;
        c.y = (a.y + b.y) % P;
        c.sumx = (a.sumx + b.sumx + a.x * b.x) % P;
        c.sumy = (a.sumy + b.sumy + a.y * b.x) % P;
        return c;
    }
};
Node pow(Node a, ll b) {
    Node ans;
    while (b) {
        if (b & 1ll) ans = ans * a;
        a = a * a;
        b >>= 1ll;
    }
    return ans;
}
Node euclid(ll p, ll q, ll r, ll n, Node U, Node R) {
    if (!n) return Node();
    if (r >= q) return pow(U, r / q) * euclid(p, q, r % q, n, U, R);
    if (p >= q) return euclid(p % q, q, r, n, U, pow(U, p / q) * R);
    ll m = (1ll * p * n + r) / q;
    if (!m) return pow(R, n);
    return pow(R, (q - r - 1) / p) * U * euclid(q, p, (q - r - 1) % p, m - 1, R, U) * pow(R, n - (q * m - r - 1) / p);
}

int main(){
    ios::sync_with_stdio(0); cin.tie(0); cout.tie(0);
    Node U, R;
    U.y = 1, R.x = 1, R.sumx = 1;
    int t;cin>>t;while (t--){
    ll l, r;cin>>l>>r;
    ll sp=ceil(phi*l);
    ll fa=(r-l+1)%P;
    if (sp<=r){
    ll ne=r-sp+1;
    fa=(fa-((ne*(l-1))%P)+4*P)%P;
    auto ans_r = euclid(a, c, b, r, U, R);
        ans_r.sumy = (ans_r.sumy + (b / c)) % P;
        auto ans_sp = euclid(a, c, b, sp-1, U, R);
        ans_sp.sumy = (ans_sp.sumy + (b / c)) % P;
        fa=(fa+ans_r.sumy-ans_sp.sumy+5*P)%P;
    }
    cout<<fa<<endl;
    }
    return 0;
}