#include <vector>
#include <iostream>
#include <algorithm>
 
using namespace std;
 
void solution(vector<int>&v) // Меняем сам вектор
{
    if(v.empty()) return;
    // Ищем min/max
    auto m = minmax_element(v.begin(),v.end());
    // Прибавляем **нужное** среднее
    int d = abs(*m.first+*m.second)/2;  // (abs(*m.first)+abs(*m.second))/2
    for_each(v.begin(),v.end(),[d](int&x){ x+= d; });
}
 
int main()
{
    vector<int> v{1,2,3,4,5,6,7,8,9};
    for(int i: v) cout << i << "  "; cout << endl;
    solution(v);
    for(int i: v) cout << i << "  "; cout << endl;
}
 

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