CF 1343 D. Constant Palindrome Sum

题目链接：https://codeforces.com/contest/1343/problem/D、

解题思路：差分来借，具体看这里

#include<bits/stdc++.h>
using namespace std;
const int maxn=4e5+10;
const int inf=1e9+10;
typedef long long ll;
int a[maxn];
int del[maxn];
int main()
{
int t;
cin>>t;
while(t--)
{
   int n,k;
   cin>>n>>k;
   memset(del,0,(2*k+10)*sizeof(int));
   for(int i=1;i<=n;i++)
   {
          cin>>a[i];
   }
   int minn,maxx;
   for(int i=1;i<=n/2;i++)
   {
          int sum=a[i]+a[n-i+1];
          minn=min(a[i],a[n-i+1]);
          maxx=(sum-minn);
          del[2]+=2;
          del[minn+1]--;
          del[maxx+k+1]++;
          del[sum]--;
          del[sum+1]++;
   } 
   int ans=del[2];
   for(int i=3;i<=2*k;i++)
   {
       del[i]+=del[i-1];
       ans=min(ans,del[i]);
   }
   cout<<ans<<endl;
}
return 0;
}