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53 lines
1.1 KiB
C++
53 lines
1.1 KiB
C++
#include <bits/stdc++.h>
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using namespace std;
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int t, a, cnt, prime[100005];
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bool flag, is_prime[1000005];
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int eratosthenes(int n) {
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int p = 0;
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for (int i = 0; i <= n; i++) is_prime[i] = 1;
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is_prime[0] = is_prime[1] = 0;
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for (int i = 2; i <= n; i++) {
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if (is_prime[i]) {
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prime[p++] = i;
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if (1ll * i * i <= n) {
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for (int j = i * i; j <= n; j += i) {
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is_prime[j] = 0;
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}
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}
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}
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}
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return p;
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}
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long long binpow(long long a, long long b, long long m) {
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a %= m;
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long long res = 1;
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while (b > 0) {
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if (b & 1) res = res * a % m;
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a = a * a % m;
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b >>= 1;
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}
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return res;
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}
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int main() {
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cin >> t;
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cnt = eratosthenes(1000000);
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while (t--) {
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flag = false;
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cin >> a;
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for (int i = 0; i < cnt; i++) {
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if (binpow(a, prime[i], 10) % 10 == binpow(prime[i], a, 10) % 10) {
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cout << prime[i] << endl;
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flag = true;
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break;
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}
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}
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if (!flag) cout << -1 << endl;
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}
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return 0;
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}
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