Question i dont understand

This is a discussion on Question i dont understand within the C++ Programming forums, part of the General Programming Boards category; Hi guys, i recieved a question for homework. I dont really understand what its asking me to do. Question: Code: ...

  1. #1
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    Question i dont understand

    Hi guys, i recieved a question for homework. I dont really understand what its asking me to do.

    Question:
    Code:
    bool balanced(vector <char> p)
    // Precondition: p[0]...p[n-1] contains n characters, each of which
    // is (, ), { or }.
    // Postcondition: The function returns true if the characters form a
    // sequence of correctly balanced parentheses with each ( matching
    // a ) and each { matching a }. Note that a sequence such as
    // ( { ) } is NOT balanced because when we draw lines to match the
    // parentheses to their partners, the lines cross each other. On the
    // other hand, ( { } ) amd { ( ) } are both balanced.
    if someone can explain what its trying to ask for, that would be much appreciated.
    PS. im not asking someone to do it for me, just explain what its trying to say cheers

  2. #2
    The larch
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    What part have you problems understanding with?

    The function takes a vector of characters and outputs whether the sequence of characters has a certain property (matched pairs of braces - as in C++ where all opening braces must have a closing brace).

    It's not enough, though, just to count each character as you are also interested in their order. A stack-like data structure can be useful.
    I might be wrong.

    Thank you, anon. You sure know how to recognize different types of trees from quite a long way away.
    Quoted more than 1000 times (I hope).

  3. #3
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    Quote Originally Posted by anon View Post
    What part have you problems understanding with?

    The function takes a vector of characters and outputs whether the sequence of characters has a certain property (matched pairs of braces - as in C++ where all opening braces must have a closing brace).

    It's not enough, though, just to count each character as you are also interested in their order. A stack-like data structure can be useful.

    did u mean something like this:
    Code:
       p.push_back('(');
       p.push_back(')');
       //THESE ARE ARE IN SEQUENCE
      
       p.push_back('{');
       p.push_back('}');
      //THESE ARE ARE IN SEQUENCE
    
       p.push_back('{');
       p.push_back('{');
    //ARE NOT IN SEQUENCE, THEREFORE DO NOT BALANCE ?

  4. #4
    The larch
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    No, the vector may contain one or more opening braces in a row. The question is - are they closed in a proper order.

    Here are some examples:
    Code:
    balanced:
    ({}{})
    ({()}())
    
    unbalanced
    ({} - unclosed brace
    ({)} - expected } instead of )
    )( - can't have closing brace before opening brace
    I might be wrong.

    Thank you, anon. You sure know how to recognize different types of trees from quite a long way away.
    Quoted more than 1000 times (I hope).

  5. #5
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    Quote Originally Posted by anon View Post
    No, the vector may contain one or more opening braces in a row. The question is - are they closed in a proper order.

    Here are some examples:
    Code:
    balanced:
    ({}{})
    ({()}())
    
    unbalanced
    ({} - unclosed brace
    ({)} - expected } instead of )
    )( - can't have closing brace before opening brace
    ahh yes.. i understand now... thanks alot anon

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