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GENIE SEQUENCE(SPOJ)

Here is the my solution :-

//siddharth prasad

#include <iostream>

#include <cstdio>

#include <cstdlib>

#include <vector>

#include <cstring>

#include <functional>

#include <algorithm>

#include <cmath>

using namespace std;

#define ALL(c) c.begin(), c.end()

#define FOR(i,c) for(typeof(c.begin())i=c.begin();i!=c.end();++i)

#define REP(i,n) for(int i=0;i<n;++i)

#define fst first

#define snd second

#define max(a,b)(a>b?a:b)

int main()

{

 int t;

 cin>>t;

 while(t--)

 {

  int n,i,flag=0,x;

  cin>>n;

  int a[1000]={0};

  for(i=0;i<n;i++)

  {

  cin>>x;

  if(a[x+1]==0)

  {

   a[x+1]=1;

   flag++;

  }

  else if(a[n-x]==0)

  {

   a[n-x]=1;

   flag++;

  }

  }

  if(flag==n)

  {

  cout<<"YES"<<endl;

  }

  else

  {

  cout<<"NO"<<endl;

  }

 }

 return 0;

}