static boolean checkPermutation ( int [ ] arr , int n ) {
  int sum = 0 ;
  for ( int i = 0 ;
  i < n ;
  i ++ ) sum += arr [ i ] ;
  int [ ] prefix = new int [ n + 1 ] ;
  Arrays . fill ( prefix , 0 ) ;
  prefix [ 0 ] = arr [ 0 ] ;
  for ( int i = 1 ;
  i < n ;
  i ++ ) prefix [ i ] = prefix [ i - 1 ] + arr [ i ] ;
  for ( int i = 0 ;
  i < n - 1 ;
  i ++ ) {
    int lsum = prefix [ i ] ;
    int rsum = sum - prefix [ i ] ;
    int l_len = i + 1 , r_len = n - i - 1 ;
    if ( ( ( 2 * lsum ) == ( l_len * ( l_len + 1 ) ) ) && ( ( 2 * rsum ) == ( r_len * ( r_len + 1 ) ) ) ) return true ;
  }
  return false ;
}

static boolean checkPermutation ( int [ ] arr , int n ) { int sum = 0 ; for ( int i = 0 ; i < n ; i ++ ) sum += arr [ i ] ; int [ ] prefix = new int [ n + 1 ] ; Arrays . fill ( prefix , 0 ) ; prefix [ 0 ] = arr [ 0 ] ; for ( int i = 1 ; i < n ; i ++ ) prefix [ i ] = prefix [ i - 1 ] + arr [ i ] ; for ( int i = 0 ; i < n - 1 ; i ++ ) { int lsum = prefix [ i ] ; int rsum = sum - prefix [ i ] ; int l_len = i + 1 , r_len = n - i - 1 ; if ( ( ( 2 * lsum ) == ( l_len * ( l_len + 1 ) ) ) && ( ( 2 * rsum ) == ( r_len * ( r_len + 1 ) ) ) ) return true ; } return false ; }
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