National Olympiad in Informatics, China, 2000

Day 1, Problem 2 - Program Parser

The Tiny Basm programming language (abbreviated the TB programming language) expressed in Backus-Naur Form (BNF) is:

            <program> ::= <statement> [newline] { <statement> [newline] }
          <statement> ::= <line-number> [space] { <statement-body> [space] }
     <statement-body> ::= <increment-statement> | <output-statement> | <branch-statement> | <condition-statement> | <end-statement>
<increment-statement> ::= <variable> + <integer>
   <output-statement> ::= <variable> ?
   <branch-statement> ::= GO [space] <line-number>
<condition-statement> ::= IF [space] <variable> = <integer> [space] <branch-statement>
      <end-statement> ::= END
           <variable> ::= <letter>
        <line-number> ::= <integer>
            <integer> ::= <digit> { <digit> }
             <letter> ::= A|B|C|D|E|F|G|H|I|J|K|L|M|N|O|P|Q|R|S|T|U|V|W|X|Y|Z
              <digit> ::= 0|1|2|3|4|5|6|7|8|9

Note: "::=" indicates a definition. "|" denotes or. An expression enclosed in curly braces {} indicates that it may occur 0 or more times. "[newline]" represents an end of line character (ASCII code 10). "[space]" represents a space character (ASCII code 32).

The following are examples of statements with incorrect formats (there will not be incorrect statements in the input):

10 A+1.5            (Does not comply with the increment-statement definition - the value is not an integer)
20 A ?              (Does not comply with the output-statement definition - there is an extra added space)
30 IF A=B GO 10     (Does not comply with the conditional-statement definition - <variable> = <variable> is invalid)

Execution of TB programs:

  • The process starts executing at the smallest line number; until a condition-statement is encountered, execution will be in ascending order of line number.
  • All variables are initialized to 0 before the program begins execution.
  • An increment-statement takes the variable in the statement and adds it to the integer, finally storing it back into the variable.
  • An output-statement takes the value in the specified variable and displays it to the screen.
  • When executing condition-statements, if and only if the variable and the integer immediately following it are equivalent, the branch-statement following it will be executed. All integers in branch-statements will be at most 4 digits long.
  • After a branch-statement has been executed, the program will jump to the line with the line number following "GO".
  • After an end-statement has been executed, the entire program will terminate.
  • Assume that the system will be able to process integers of any size, and overflows will not occur.

Please write a program that, given a program P in the TB programming language, finds the number of statements that will be executed upon running the program (whether or not a conditional-statement successfully branches, it will count as one executed statement).

Input Format

The input will contain one program P in the TB programming language, with no more than 100 total lines of statements.
No statement within P will exceed a length of 20 characters.
Within P's branch-statements, there will always be a statement corresponding to the line number following GO.
P may contain many different end-statements.
Within P, the statement with the largest line number will always be an end-statement.
No line number in P will exceed 3000.
The input will not necessarily give the lines of P in increasing order of line number.

Output Format

The output should contain one line with one integer. If the program can properly terminate, output the number of executed statements. If the program cannot properly terminate, output -1.

Note: It is guaranteed that the answer will never exceed 5 million.

Sample Input

10 A+1
20 IF A=5 GO 60
60 END
30 A+2
40 A?
50 GO 20

Sample Output



The order in which the lines are executed are: 10→20→30→40→50→20→30→40→50→20→60, for a total of 11 executed statements.

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Best Solutions

Point Value: 12 (partial)
Time Limit: 1.00s
Memory Limit: 16M
Added: May 06, 2014

Languages Allowed:

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