Submission #356078

#	Time	Username	Problem	Language	Result	Execution time	Memory
356078		parsabahrami	Three Friends (BOI14_friends)	C++17	0 / 100	171 ms	20972 KiB

friends

// Call my Name and Save me from The Dark
#include <bits/stdc++.h>
 
using namespace std;

typedef long long int ll;
typedef pair<int, int> pii;
 
#define SZ(x)                       (int) x.size()
#define F                           first
#define S                           second

const int N = 2e6 + 10, MOD = 1e9 + 7;
int n, H[N], pw[N], base = 31; char S[N]; vector<int> R;

int get(int l, int r) {
    if (r < l) return 0;
    return (H[r] - 1ll * H[l - 1] * pw[r - l + 1] % MOD + MOD) % MOD;
}

int main() {
    pw[0] = 1;
    for (int i = 1; i < N; i++) pw[i] = 1ll * base * pw[i - 1] % MOD;
    scanf("%d%s", &n, S + 1);
    if (n % 2 == 0) return !printf("NOT POSSIBLE\n");
    for (int i = 1; i <= n; i++) {
        H[i] = (1ll * H[i - 1] * base % MOD + S[i] - 'A' + 1) % MOD;
    }
    for (int i = 1; i <= n; i++) {
        if (i > n / 2) {
            int h = get(1, n / 2), l = get(n / 2 + 1, i - 1), r = get(i + 1, n);
            int hsh = (1ll * l * pw[n - i] % MOD + r) % MOD;
            if (h == hsh) R.push_back(i);
        } else {
            int h = get(n / 2 + 2, n), l = get(1, i - 1), r = get(i + 1, n / 2 + 1);
            l = (1ll * l * pw[n / 2 - i + 1] % MOD + r) % MOD;
            if (h == l) R.push_back(i);
        }
    }   
    if (!SZ(R)) printf("NOT POSSIBLE\n");
    else if (SZ(R) > 1) printf("NOT UNIQUE\n");
    else {
        int id = R[0];
        for (int i = 1, j = 0; i <= n && j < n / 2; i++) {
            if (i == id) continue;
            else {
                printf("%c", S[i]), j++;
            }
        }
    }
    return 0;
}

Compilation message (stderr)

friends.cpp: In function 'int main()':
friends.cpp:24:10: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
   24 |     scanf("%d%s", &n, S + 1);
      |     ~~~~~^~~~~~~~~~~~~~~~~~~

• Subtask 1: 0 / 35
• Subtask 2: 0 / 65