static int numberOfPermutations ( int a [ ] , int n ) {
  int sumEven , sumOdd , c = 0 ;
  do {
    sumEven = sumOdd = 0 ;
    for ( int i = 0 ;
    i < n ;
    i ++ ) {
      if ( i % 2 == 0 ) {
        sumOdd += a [ i ] ;
      }
      else {
        sumEven += a [ i ] ;
      }
    }
    if ( sumOdd == sumEven ) {
      c ++ ;
    }
  }
  while ( next_permutation ( a ) ) ;
  return c ;
}

static int numberOfPermutations ( int a [ ] , int n ) { int sumEven , sumOdd , c = 0 ; do { sumEven = sumOdd = 0 ; for ( int i = 0 ; i < n ; i ++ ) { if ( i % 2 == 0 ) { sumOdd += a [ i ] ; } else { sumEven += a [ i ] ; } } if ( sumOdd == sumEven ) { c ++ ; } } while ( next_permutation ( a ) ) ; return c ; }
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