leetcode_potd/3405 at main · G-Rajashekar/leetcode_potd · GitHub

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int mod=1e9+7;
class Solution {
public:
    long long findPow(long long a,long long b){
        if (b==0) return 1;
        long long half=findPow(a,b/2);

        long long res=(half*half)%mod;

        if (b%2==1) {
            res=(res*a)%mod;
        }
        return res;
    }
    int countGoodArrays(int n, int m, int k) {
        vector<long long>fact(n+1);
        vector<long long>invFact(n+1,1);

        fact[0]=1;
        fact[1]=1;

        for (int i=2;i<=n;i++){
            fact[i]=(i*fact[i-1])%mod;
        }

        for (int i=0;i<=n;i++){
            invFact[i]=findPow(fact[i],mod-2)%mod;
        }

        long long res1=(fact[n-1]%mod*invFact[k]%mod*invFact[n-k-1]%mod)%mod;
        long long res2=(res1*m)%mod;
        long long finalResult=(res2*findPow(m-1,n-k-1)%mod)%mod;

        return finalResult;
    }
};

TC:O(N+LOG(N-K-1))
SC:O(N)