代码如下:
#include <bits/stdc++.h>
using namespace std;
//中间数
int main(){
int n;
cin >> n;
vector<int> v(n);
for(int i = 0; i < n; i++){
cin >> v[i];
}
sort(v.begin(), v.end());
int m = n / 2, num = 1;
if(n%2 == 0 && v[m] != v[m-1]){
cout << -1 << endl;
return 0;
}
for(int i = m-1, j = m+1; i >= 0 || j < n;){
if(i >= 0 && v[i] == v[m]){
i--;
num++;
}
else i = -1;
if(j < n && v[j] == v[m]){
j++;
num++;
}
else j = n;
}
if((n-num)%2 == 0) cout << v[m] << endl;
else cout << -1 << endl;
return 0;
}