老师的答案（doge）来抄吧

#include<bits/stdc++.h>
using namespace std;
int  main(){
	int t,n,m;
    cin >> t;
    while(t--){
        cin>>n>>m;
        long long m1=m;
        for(int i = 1;i<n;i++){
            m1=(m1*(m-1))%998244353;
        }
        cout << m1<<endl;
    }
    
}