#include <bits/stdc++.h> using namespace std; const int MAXN=2e6+6; int cont[MAXN][30], cont2[MAXN][30]; char v[MAXN]; int n; int main() { scanf("%d", &n); scanf(" %s", &v[1]); for(int i=1; i<=n; i++) { for(int j=0; j<=28; j++) cont[i][j]=cont[i-1][j]; cont[i][v[i]-'A']++; } for(int i=n; i>=1; i--) { for(int j=0; j<=28; j++) cont2[i][j]=cont2[i+1][j]; cont2[i][v[i]-'A']++; } int resp=-1; for(int i=1; i<=n; i++) { bool ok=1; for(int j=0; j<=28; j++) { if(i<=(n+1)/2) { int val=cont[(n+1)/2][j]; int val2=cont2[(n+1)/2+1][j]; if(j==v[i]-'A') val--; // printf("test %d letra %d > %d %d\n", i, j, val, val2); if(val!=val2) { ok=0; break; } } else { int val=cont[n/2][j]; int val2=cont2[(n+1)/2][j]; if(j==v[i]-'A') val2--; if(val!=val2) { ok=0; break; } } } if(ok) { // printf("ok %d\n", i); if(resp!=-1) { printf("NOT UNIQUE\n"); return 0; } resp=i; } } if(resp==-1) { printf("NOT POSSIBLE\n"); } else { if(resp<=(n+1)/2) { for(int i=1; i<=(n+1)/2; i++) { if(i==resp) continue; printf("%c", v[i]); } } else { for(int i=1; i<=n/2; i++) { printf("%c", v[i]); } } } }

friends.cpp: In function 'int main()':
friends.cpp:10:7: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
  scanf("%d", &n);
  ~~~~~^~~~~~~~~~
friends.cpp:11:7: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
  scanf(" %s", &v[1]);
  ~~~~~^~~~~~~~~~~~~~