Language: C++

/*
Though leaves are many , the root is one.
Through all the lying days of my youth
I swayed my leaves and flowers in the sun.
Now I may wither into the truth.
	  	  	- William Butler Yeats
*/
#pragma GCC optimize("Ofast,no-stack-protector")
#pragma GCC target("sse,sse2,sse3,ssse3,sse4,popcnt,abm,mmx")
#pragma GCC target("avx,tune=native")
#include<bits/stdc++.h>
//#pragma comment("-Wl,--stack=1024000000")
//#include<ext/pb_ds/assoc_container.hpp>
using namespace std;
namespace fastio{
    char in[100000];
    int itr=0,llen=0;
    char get(){
        if(itr==llen)llen=fread(in,1,100000,stdin),itr=0;
        if(llen==0)return EOF;
        return in[itr++];
    }
    char out[100000];
    int itr2=0;
    void put(char c){
        out[itr2++]=c;
        if(itr2==100000){
            fwrite(out,1,100000,stdout);
            itr2=0;
        }
    }
    int clear(){
        fwrite(out,1,itr2,stdout);
        itr2=0;
        return 0;
    }
    int getint(){
        int ret=0;char ch=get();
        if(ch=='-')return -getint();
        while (ch<'0'||ch>'9'){
            ch=get();if(ch=='-')return -getint();
        }
        while ('0'<=ch&&ch<='9'){
            ret=ret*10-48+ch;
            ch=get();
        }
        return ret;
    }
    string getstr(){
        string ret="";
        char ch=get();
        while(ch==' '||ch=='\n')ch=get();
        while(ch!=' '&&ch!='\n')ret.push_back(ch),ch=get();
        return ret;
    }
    void putstr(string s){
        for(int i=0;i<s.size();i++)put(s[i]);
    }
    void putint(int x){
        if(x<0){
            put('-');
            putint(-x);
            return;
        }
        if(x==0){
            put('0');put(' ');
            return;
        }
        char c[40];int pos=0;
        while(x){
            c[pos++]='0'+x%10;
            x/=10;
        }
        for(int i=pos-1;i>=0;i--)put(c[i]);
        put(' ');
    }
    void putln(int x){
        if(x<0){
            put('-');
            putln(-x);
            return;
        }
        if(x==0){
            put('0');put('\n');
            return;
        }
        char c[40];int pos=0;
        while(x){
            c[pos++]='0'+x%10;
            x/=10;
        }
        for(int i=pos-1;i>=0;i--)put(c[i]);
        put('\n');
    }
}
using namespace fastio;
//using namespace __gnu_pbds;
const int inf=0x3f3f3f3f;
const double eps=1e-6;
const int mod=1000000007;
typedef long long ll;
#ifndef LOCAL
#define cerr if(0)cout
#define eprintf(...) 0
#else
#define eprintf(...) fprintf(stderr, __VA_ARGS__)
#endif
inline string getstr(string &s,int l,int r){string ret="";for(int i=l;i<=r;i++)ret.push_back(s[i]);return ret;}
int modpow(int x,int y,int md=mod){int ret=1;do{if(y&1)ret=(ll)ret*x%md;x=(ll)x*x%md;}while(y>>=1);return ret;}
inline int Rand(){return rand()*32768+rand();}
int n,a[200005],b[200005],s[200005],d[200005];
int C[4005][4005],sum[6666];
int main(){
	n=getint();
	for(int i=1;i<=n;i++){
		a[i]=getint();b[i]=getint();s[i]=a[i]+b[i];
	}
	C[0][0]=1;
	for(int i=1;i<=4000;i++){
		C[i][0]=C[i][i]=1;
		for(int j=1;j<i;j++){
			C[i][j]=(C[i-1][j]+C[i-1][j-1])%mod;
		}
	}
	int ans=0;
	for(int delta=-2000;delta<=2000;delta++){
		const int pos=delta+2222;
		for(int j=1;j<=n;j++){
			if(delta+a[j]>=0&&delta<=b[j]){
				cerr<<delta<<" "<<j<<" "<<C[a[j]+b[j]][a[j]+delta]<<endl;
				sum[pos]+=C[a[j]+b[j]][a[j]+delta];
				if(sum[pos]>=mod)sum[pos]-=mod;
			}
		}
	}
	for(int i=-2000;i<=0;i++){
		ans+=(ll)(1ll+(i!=0?1ll:0ll))*sum[i+2222]*sum[-i+2222]%mod;
		ans%=mod;
	}
	for(int i=1;i<=n;i++){
		ans-=C[a[i]+a[i]+b[i]+b[i]][a[i]+a[i]];
		if(ans<0)ans+=mod;
	}
	ans=((ll)ans*(mod+1)/2)%mod;
	cout<<ans<<endl;
	return 0;
}

Compiler output:
In file included from /usr/include/c++/14/string:43,
                 from /usr/include/c++/14/bitset:52,
                 from /usr/include/x86_64-linux-gnu/c++/14/bits/stdc++.h:52,
                 from a.cc:11:
/usr/include/c++/14/bits/allocator.h: In destructor 'std::__cxx11::basic_string<char>::_Alloc_hider::~_Alloc_hider()':
/usr/include/c++/14/bits/allocator.h:182:7: error: inlining failed in call to 'always_inline' 'std::allocator< <template-parameter-1-1> >::~allocator() noexcept [with _Tp = char]': target specific option mismatch
  182 |       ~allocator() _GLIBCXX_NOTHROW { }
      |       ^
In file included from /usr/include/c++/14/string:54:
/usr/include/c++/14/bits/basic_string.h:186:14: note: called from here
  186 |       struct _Alloc_hider : allocator_type // TODO check __is_final
      |              ^~~~~~~~~~~~