Decrypt

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

int per[26],res[26];
int tmp[26];

void mul1() {
	for (int i=0;i<26;i++) {
		if (per[i]==-1 || per[per[i]]==-1) tmp[i]=-1;
		else tmp[i]=per[per[i]];
	}
	for (int i=0;i<26;i++) per[i]=tmp[i];
}

void mul2() {
	for (int i=0;i<26;i++) {
		if (per[i]==-1) tmp[i]=-1;
		else tmp[i]=res[per[i]];
	}
	for (int i=0;i<26;i++) res[i]=tmp[i];
}

void pot(int k) {
	for (int i=0;i<26;i++) res[i]=i;
	while (k) {
		if (k&1) mul2();
		mul1();
		k>>=1;
	}
}

int main() {
	for (int i=0;i<26;i++) per[i]=-1;
	string f,s;
	int k;
	cin>>f>>k>>s;
	for (int i=0;i<26;i++) {
		if (per[f[i]-'a']>=0) per[f[i]-'a']=-2;
		if (per[f[i]-'a']==-1) per[f[i]-'a']=i;
	}
	for (int i=0;i<26;i++) per[i]=max(per[i],-1);
	pot(k);
	for (char c : s) {
		if (res[c-'a']==-1) {
			cout<<"impossible\n";
			return 0;
		}
	}
	for (char c : s) {
		cout<<(char)(res[c-'a']+'a');
	}
	cout<<"\n";
}

Test 1

Verdict: ACCEPTED

Test 2

Verdict: ACCEPTED

Test 3

Verdict: ACCEPTED

Test 4

Verdict: ACCEPTED

Test 5

Verdict: ACCEPTED

Test 6

Verdict: ACCEPTED

Test 7

Verdict: ACCEPTED

Test 8

Verdict: ACCEPTED

Test 9

Verdict: ACCEPTED

Test 10

Verdict: ACCEPTED

Test 11

Verdict: ACCEPTED

Test 12

Verdict: ACCEPTED

Test 13

Verdict: ACCEPTED

Test 14

Verdict: ACCEPTED

Test 15

Verdict: ACCEPTED

Test 16

Verdict: ACCEPTED

Test 17

Verdict: ACCEPTED

Test 18

Verdict: ACCEPTED

Test 19

Verdict: ACCEPTED

Test 20

Verdict: ACCEPTED

Test 21

Verdict: ACCEPTED

Test 22

Verdict: ACCEPTED

Test 23

Verdict: ACCEPTED

Test 24

Verdict: ACCEPTED

Test 25

Verdict: ACCEPTED

Test 26

Verdict: ACCEPTED

Test 27

Verdict: ACCEPTED

Test 28

Verdict: ACCEPTED

Test 29

Verdict: ACCEPTED

Test 30

Verdict: ACCEPTED