Submission #356096

#	Time	Username	Problem	Language	Result	Execution time	Memory
356096		parsabahrami	Three Friends (BOI14_friends)	C++17	0 / 100	212 ms	34796 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[] = {696969569, (int) 1e9 + 9};
int n, H[2][N], pw[2][N], base = 70; char S[N]; vector<int> R;

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

int main() {
    pw[0][0] = pw[1][0] = 1;
    for (int i = 1; i < N; i++) for (int j = 0; j < 2; j++) pw[j][i] = 1ll * base * pw[j][i - 1] % MOD[j];
    scanf("%d%s", &n, S + 1);
    if (n % 2 == 0) return !printf("NOT POSSIBLE\n");
    for (int i = 1; i <= n; i++) {
        for (int j = 0; j < 2; j++) H[j][i] = (1ll * H[j][i - 1] * base % MOD[j] + S[i] - 'A' + 1) % MOD[j];
    }
    for (int i = 1; i <= n; i++) {
        if (i > n / 2) {
            pii h = get(1, n / 2), l = get(n / 2 + 1, i - 1), r = get(i + 1, n);
            l = {(1ll * l.F * pw[0][n - i] % MOD[0] + r.F) % MOD[0], (1ll * l.S * pw[1][n - i] % MOD[1] + r.S) % MOD[1]};
            if (h == l) R.push_back(i);
        } else {
            pii h = get(n / 2 + 2, n), l = get(1, i - 1), r = get(i + 1, n / 2 + 1);
            l = {(1ll * l.F * pw[0][n / 2 - i + 1] % MOD[0] + r.F) % MOD[0], (1ll * l.S * pw[1][n / 2 - i + 1] % MOD[1] + r.S) % MOD[1]};
            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:27:10: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
   27 |     scanf("%d%s", &n, S + 1);
      |     ~~~~~^~~~~~~~~~~~~~~~~~~

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