public static int findOccurrences ( String str1 , String substr1 ) {
  int n = str1 . length ( ) ;
  char [ ] str = str1 . toCharArray ( ) ;
  char [ ] substr = substr1 . toCharArray ( ) ;
  int [ ] preLeft = new int [ n ] ;
  int [ ] preRight = new int [ n ] ;
  if ( str [ 0 ] == substr [ 0 ] ) preLeft [ 0 ] ++ ;
  for ( int i = 1 ;
  i < n ;
  i ++ ) {
    if ( str [ i ] == substr [ 0 ] ) preLeft [ i ] = preLeft [ i - 1 ] + 1 ;
    else preLeft [ i ] = preLeft [ i - 1 ] ;
  }
  if ( str [ n - 1 ] == substr [ 2 ] ) preRight [ n - 1 ] ++ ;
  for ( int i = n - 2 ;
  i >= 0 ;
  i -- ) {
    if ( str [ i ] == substr [ 2 ] ) preRight [ i ] = preRight [ i + 1 ] + 1 ;
    else preRight [ i ] = preRight [ i + 1 ] ;
  }
  int counter = 0 ;
  for ( int i = 1 ;
  i < n - 1 ;
  i ++ ) {
    if ( str [ i ] == str [ 1 ] ) {
      int total = preLeft [ i - 1 ] * preRight [ i + 1 ] ;
      counter += total ;
    }
  }
  return counter ;
}

public static int findOccurrences ( String str1 , String substr1 ) { int n = str1 . length ( ) ; char [ ] str = str1 . toCharArray ( ) ; char [ ] substr = substr1 . toCharArray ( ) ; int [ ] preLeft = new int [ n ] ; int [ ] preRight = new int [ n ] ; if ( str [ 0 ] == substr [ 0 ] ) preLeft [ 0 ] ++ ; for ( int i = 1 ; i < n ; i ++ ) { if ( str [ i ] == substr [ 0 ] ) preLeft [ i ] = preLeft [ i - 1 ] + 1 ; else preLeft [ i ] = preLeft [ i - 1 ] ; } if ( str [ n - 1 ] == substr [ 2 ] ) preRight [ n - 1 ] ++ ; for ( int i = n - 2 ; i >= 0 ; i -- ) { if ( str [ i ] == substr [ 2 ] ) preRight [ i ] = preRight [ i + 1 ] + 1 ; else preRight [ i ] = preRight [ i + 1 ] ; } int counter = 0 ; for ( int i = 1 ; i < n - 1 ; i ++ ) { if ( str [ i ] == str [ 1 ] ) { int total = preLeft [ i - 1 ] * preRight [ i + 1 ] ; counter += total ; } } return counter ; }
(method_declaration (modifiers) type: (integral_type) name: (identifier) parameters: (formal_parameters (formal_parameter type: (type_identifier) name: (identifier)) (formal_parameter type: (type_identifier) name: (identifier))) body: (block (local_variable_declaration type: (integral_type) declarator: (variable_declarator name: (identifier) value: (method_invocation object: (identifier) name: (identifier) arguments: (argument_list)))) (local_variable_declaration type: (array_type element: (integral_type) dimensions: (dimensions)) declarator: (variable_declarator name: (identifier) value: (method_invocation object: (identifier) name: (identifier) arguments: (argument_list)))) (local_variable_declaration type: (array_type element: (integral_type) dimensions: (dimensions)) declarator: (variable_declarator name: (identifier) value: (method_invocation object: (identifier) name: (identifier) arguments: (argument_list)))) (local_variable_declaration type: (array_type element: (integral_type) dimensions: (dimensions)) declarator: (variable_declarator name: (identifier) value: (array_creation_expression type: (integral_type) dimensions: (dimensions_expr (identifier))))) (local_variable_declaration type: (array_type element: (integral_type) dimensions: (dimensions)) declarator: (variable_declarator name: (identifier) value: (array_creation_expression type: (integral_type) dimensions: (dimensions_expr (identifier))))) (if_statement condition: (parenthesized_expression (binary_expression left: (array_access array: (identifier) index: (decimal_integer_literal)) right: (array_access array: (identifier) index: (decimal_integer_literal)))) consequence: (expression_statement (update_expression (array_access array: (identifier) index: (decimal_integer_literal))))) (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 (binary_expression left: (array_access array: (identifier) index: (identifier)) right: (array_access array: (identifier) index: (decimal_integer_literal)))) consequence: (expression_statement (assignment_expression left: (array_access array: (identifier) index: (identifier)) right: (binary_expression left: (array_access array: (identifier) index: (binary_expression left: (identifier) right: (decimal_integer_literal))) right: (decimal_integer_literal)))) alternative: (expression_statement (assignment_expression left: (array_access array: (identifier) index: (identifier)) right: (array_access array: (identifier) index: (binary_expression left: (identifier) right: (decimal_integer_literal)))))))) (if_statement condition: (parenthesized_expression (binary_expression left: (array_access array: (identifier) index: (binary_expression left: (identifier) right: (decimal_integer_literal))) right: (array_access array: (identifier) index: (decimal_integer_literal)))) consequence: (expression_statement (update_expression (array_access array: (identifier) index: (binary_expression left: (identifier) right: (decimal_integer_literal)))))) (for_statement init: (local_variable_declaration type: (integral_type) declarator: (variable_declarator name: (identifier) value: (binary_expression left: (identifier) right: (decimal_integer_literal)))) condition: (binary_expression left: (identifier) right: (decimal_integer_literal)) update: (update_expression (identifier)) body: (block (if_statement condition: (parenthesized_expression (binary_expression left: (array_access array: (identifier) index: (identifier)) right: (array_access array: (identifier) index: (decimal_integer_literal)))) consequence: (expression_statement (assignment_expression left: (array_access array: (identifier) index: (identifier)) right: (binary_expression left: (array_access array: (identifier) index: (binary_expression left: (identifier) right: (decimal_integer_literal))) right: (decimal_integer_literal)))) alternative: (expression_statement (assignment_expression left: (array_access array: (identifier) index: (identifier)) right: (array_access array: (identifier) index: (binary_expression left: (identifier) right: (decimal_integer_literal)))))))) (local_variable_declaration type: (integral_type) declarator: (variable_declarator name: (identifier) value: (decimal_integer_literal))) (for_statement init: (local_variable_declaration type: (integral_type) declarator: (variable_declarator name: (identifier) value: (decimal_integer_literal))) condition: (binary_expression left: (identifier) right: (binary_expression left: (identifier) right: (decimal_integer_literal))) update: (update_expression (identifier)) body: (block (if_statement condition: (parenthesized_expression (binary_expression left: (array_access array: (identifier) index: (identifier)) right: (array_access array: (identifier) index: (decimal_integer_literal)))) consequence: (block (local_variable_declaration type: (integral_type) declarator: (variable_declarator name: (identifier) value: (binary_expression left: (array_access array: (identifier) index: (binary_expression left: (identifier) right: (decimal_integer_literal))) right: (array_access array: (identifier) index: (binary_expression left: (identifier) right: (decimal_integer_literal)))))) (expression_statement (assignment_expression left: (identifier) right: (identifier))))))) (return_statement (identifier))))