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  • Codeforces 612C Replace To Make Regular Bracket Sequence【栈】

    time limit per test
    1 second
    memory limit per test
    256 megabytes
    input
    standard input
    output
    standard output

    You are given string s consists of opening and closing brackets of four kinds <>{}[](). There are two types of brackets: opening and closing. You can replace any bracket by another of the same type. For example, you can replace < by the bracket {, but you can't replace it by ) or >.

    The following definition of a regular bracket sequence is well-known, so you can be familiar with it.

    Let's define a regular bracket sequence (RBS). Empty string is RBS. Let s1 and s2 be a RBS then the strings <s1>s2{s1}s2[s1]s2,(s1)s2 are also RBS.

    For example the string "[[(){}]<>]" is RBS, but the strings "[)()" and "][()()" are not.

    Determine the least number of replaces to make the string s RBS.

    Input

    The only line contains a non empty string s, consisting of only opening and closing brackets of four kinds. The length of s does not exceed 106.

    Output

    If it's impossible to get RBS from s print Impossible.

    Otherwise print the least number of replaces needed to get RBS from s.

    Examples
    input
    [<}){}
    
    output
    2
    input
    {()}[]
    
    output
    0
    input
    ]]
    
    output
    Impossible
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  • 原文地址:https://www.cnblogs.com/cniwoq/p/6770915.html
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