题解里都在线性求，但其实不需要，也能1.61sAC，附上代码，求加入题解：

#include <cstdio>
#include <cctype>

struct istream{
    
    template <typename T>
    istream &operator>>(T &x){
        
        x = 0;
        char c = getchar_unlocked();
        
        while (!isdigit(c)) c = getchar_unlocked();
        while (isdigit(c)) x = x * 10 + c - '0',c = getchar_unlocked();;
        
        return *this;
    }
    
}cin;

const int maxn = 5e6 + 5,mod = 998244353;

auto exgcd(int a,int b){//auto->result
    
    struct result{int x,y,gcd;};
    if (b == 0) return (result){1,0,a};
    result res = exgcd(b,a % b);
    
    return (result){res.y,res.x - a / b * res.y,res.gcd};
}

int inv(int a,int p){return (exgcd(a,p).x + p) % p;}

int main(){
    
    int T,N,ans = 0,fac[maxn],ifac[maxn];
    
    cin >> T >> N;
    fac[0] = ifac[0] = 1;
    for (int i = 1;i <= N;i++){
        
        fac[i] = (long)fac[i - 1] * i % mod;
        ifac[i] = inv(fac[i],mod);
        
    }
    while (T--){
        
        int n,m;
        
        cin >> n >> m;
        ans ^= (long)fac[n] * ifac[m] % mod * ifac[n - m] % mod;/*c(n,m) = n! / (m! * (n - m)!)*/
        
    }
    printf("%d\n",ans);
    
    return 0;
}