static int count_pairs ( int n , int a [ ] ) {
  HashMap < Integer , Integer > frequency = new HashMap < > ( ) ;
  for ( int i = 0 ;
  i < n ;
  i ++ ) {
    if ( ! frequency . containsKey ( a [ i ] ) ) frequency . put ( a [ i ] , 0 ) ;
    frequency . put ( a [ i ] , frequency . get ( a [ i ] ) + 1 ) ;
  }
  int count = 0 ;
  for ( Map . Entry < Integer , Integer > x : frequency . entrySet ( ) ) {
    int f = x . getValue ( ) ;
    count += f * ( f - 1 ) / 2 ;
  }
  return ( ( n * ( n - 1 ) ) / 2 ) - count ;
}

static int count_pairs ( int n , int a [ ] ) { HashMap < Integer , Integer > frequency = new HashMap < > ( ) ; for ( int i = 0 ; i < n ; i ++ ) { if ( ! frequency . containsKey ( a [ i ] ) ) frequency . put ( a [ i ] , 0 ) ; frequency . put ( a [ i ] , frequency . get ( a [ i ] ) + 1 ) ; } int count = 0 ; for ( Map . Entry < Integer , Integer > x : frequency . entrySet ( ) ) { int f = x . getValue ( ) ; count += f * ( f - 1 ) / 2 ; } return ( ( n * ( n - 1 ) ) / 2 ) - count ; }
(method_declaration (modifiers) type: (integral_type) name: (identifier) parameters: (formal_parameters (formal_parameter type: (integral_type) name: (identifier)) (formal_parameter type: (integral_type) name: (identifier) dimensions: (dimensions))) body: (block (local_variable_declaration type: (generic_type (type_identifier) (type_arguments (type_identifier) (type_identifier))) declarator: (variable_declarator name: (identifier) value: (object_creation_expression type: (generic_type (type_identifier) (type_arguments)) arguments: (argument_list)))) (for_statement init: (local_variable_declaration type: (integral_type) declarator: (variable_declarator name: (identifier) value: (decimal_integer_literal))) condition: (binary_expression left: (identifier) right: (identifier)) update: (update_expression (identifier)) body: (block (if_statement condition: (parenthesized_expression (unary_expression operand: (method_invocation object: (identifier) name: (identifier) arguments: (argument_list (array_access array: (identifier) index: (identifier)))))) consequence: (expression_statement (method_invocation object: (identifier) name: (identifier) arguments: (argument_list (array_access array: (identifier) index: (identifier)) (decimal_integer_literal))))) (expression_statement (method_invocation object: (identifier) name: (identifier) arguments: (argument_list (array_access array: (identifier) index: (identifier)) (binary_expression left: (method_invocation object: (identifier) name: (identifier) arguments: (argument_list (array_access array: (identifier) index: (identifier)))) right: (decimal_integer_literal))))))) (local_variable_declaration type: (integral_type) declarator: (variable_declarator name: (identifier) value: (decimal_integer_literal))) (enhanced_for_statement type: (generic_type (scoped_type_identifier (type_identifier) (type_identifier)) (type_arguments (type_identifier) (type_identifier))) name: (identifier) value: (method_invocation object: (identifier) name: (identifier) arguments: (argument_list)) body: (block (local_variable_declaration type: (integral_type) declarator: (variable_declarator name: (identifier) value: (method_invocation object: (identifier) name: (identifier) arguments: (argument_list)))) (expression_statement (assignment_expression left: (identifier) right: (binary_expression left: (binary_expression left: (identifier) right: (parenthesized_expression (binary_expression left: (identifier) right: (decimal_integer_literal)))) right: (decimal_integer_literal)))))) (return_statement (binary_expression left: (parenthesized_expression (binary_expression left: (parenthesized_expression (binary_expression left: (identifier) right: (parenthesized_expression (binary_expression left: (identifier) right: (decimal_integer_literal))))) right: (decimal_integer_literal))) right: (identifier)))))