#include <iostream>
#include <vector>
#include <algorithm>
using namespace std;
int solve(vector<int> &A) {
std::sort(A.begin(), A.end());
int size1 = A.size();
bool flag = true;
for(int i =0; i <size1; i++) {
if(A[i]!=0) {flag = false; break; }
}
if(flag) return 1;
for(int i =1; i <size1; i++) {
if(A[i] == A[i-1]) continue;
if(A[i-1] == size1 - i) return 1;
}
return -1;
}
int main() {
// your code goes here
//vector<int> A = {1, 2, 7, 0, 9, 3, 6, 0, 6 };
vector<int> A = { -4, 7, 5, 3, 5, -4, 2, -1, -9, -8, -3, 0, 9, -7, -4, -10, -4, 2, 6, 1, -2, -3, -1, -8, 0, -8, -7, -3, 5, -1, -8, -8, 8, -1, -3, 3, 6, 1, -8, -1, 3, -9, 9, -6, 7, 8, -6, 5, 0, 3, -4, 1, -10, 6, 3, -8, 0, 6, -9, -5, -5, -6, -3, 6, -5, -4, -1, 3, 7, -6, 5, -8, -5, 4, -3, 4, -6, -7, 0, -3, -2, 6, 8, -2, -6, -7, 1, 4, 9, 2, -10, 6, -2, 9, 2, -4, -4, 4, 9, 5, 0, 4, 8, -3, -9, 7, -8, 7, 2, 2, 6, -9, -10, -4, -9, -5, -1, -6, 9, -10, -1, 1, 7, 7, 1, -9, 5, -1, -3, -3, 6, 7, 3, -4, -5, -4, -7, 9, -6, -2, 1, 2, -1, -7, 9, 0, -2, -2, 5, -10, -1, 6, -7, 8, -5, -4, 1, -9, 5, 9, -2, -6, -2, -9, 0, 3, -10, 4, -6, -6, 4, -3, 6, -7, 1, -3, -5, 9, 6, 2, 1, 7, -2, 5 } ;
cout << solve(A);
return 0;
}
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