58C - Trees - CodeForces Solution

#include <bits/stdc++.h>
using namespace std;
#define ll             long long int 
#define ulli           unsigned long long int 
#define li             long int 
#define ff(i,a,b)      for(int i=a;i<b;i++)
#define fb(i,b,a)      for(int i=b;i>=a;i--)
#define w(t)           while(--t >= 0)
#define l(s)           s.length()
#define ci(n)          cin>>n;
#define fast           ios_base::sync_with_stdio(false);
#define sa(a,n)        sort(a,a+n)
#define sv(v)          sort(v.begin(),v.end())
#define cy             cout<<"YES\n"
#define cn             cout<<"NO\n"
#define nl             cout<<"\n"
#define minus          cout<<"-1\n";
#define vi             vector<int>
#define pb             push_back
#define tc             int t; cin>>t;
#define pp             pair<int,int>
#define input(a,n)     for(int i=0;i<n;i++) cin>>a[i];
#define mod            1000000007
#define co(n)          cout<<n;
#define ret            return 0
#define mi             map<int,int>
#define output(a,n)    for(int i=0;i<n;i++) cout<<a[i]<<" ";   
#define forn(i, n)     ff(i, 0, n)
#define sz(v)          int((v).size())

int main() 
{
    fast;
	int n;
	cin>>n;
	int a[n+1];
	for(int i = 1; i <= n; i++) 
	{
		cin>>a[i];
	}
	int x = 0;
	map<int, int> map;
	int i=1, j=n;
	while(i <= j) 
	{
		map[a[i] - x]++;
		if(i != j)
		{
			map[a[j] - x]++;
		}
		x++;
		i++;
		j--;
	}
	int mx = 0;
	for(auto p : map)
	{
		if(p.first) 
		{
			mx = max(mx, p.second);
		}
	}
 	cout<<n-mx;
}