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#include <bits/stdc++.h>
using namespace std;
 
#define ll long long
 
const int maxn = 2e5+10;
int n,k,a[maxn];
void solution() {
	cin >> n >> k;
	for (int i=0; i<n; i++) {
		cin >> a[i];
	}
 
 
	map<int,int> xd;
	for (int i=0; i<n/2; i++) {
		xd[a[i]+a[n-i-1]]++;
	}
 
	int ansf = 4e5;
 
	for (auto& e : xd) {
		int ans = 0;
		int x = e.first;	
		for (int i=0; i<n/2; i++) {
			int xc = a[i] + a[n-i-1];
			if (xc == x)
				continue;
			if (xc > x) {
				int rem = xc-x;
				if (a[i]-rem >= 0) {
					ans++;
				}
				else if (a[n-i-1]-rem >= 0) {
					ans++;
				}
				else {
					ans += 2;
				}
			}
			else {
				int rem = x-xc;
 
				if (a[i]+rem <= k) {
					ans++;
				}
				else if (a[n-i-1]+rem <= k) {
					ans++;
				}
				else {
					ans+=2;
				}
 
			}
		}
		ansf = min(ansf, ans);
	}
	cout << ansf << endl;
 
}
 
int main() {
 
	int t;
	cin >> t;
	while (t--) {
		solution();
	}
 
	return 0;
}

Runtime error #stdin #stdout 0.01s 4372KB

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Standard input is empty

stdout

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https://ideone.com/XJrXEx

language:

C++14 (gcc 8.3)

created:

visibility:

public

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