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I/O formats

Input format specifies two things at the same time:

  • How the input variable values should be printed to official test case input files.
  • How the sample test case input files should be parsed into input variables, as they are specified as literal strings. If some sample sample test cases can't be parsed, it means that you have written invalid sample test cases, and the whole generation will fail.

Output format specifies how the output files should be parsed into output variables. If the output files can't be parsed, it means that you have written invalid solution program, and the whole generation will fail.

Each of the I/O formats is defined as a list of I/O segments in InputFormat() and OutputFormat() methods of the problem specification class, respectively, as follows.

void InputFormat() {
    // list of input segments
}

void OutputFormat() {
    // list of output segments
}

Each I/O segment is specified by a function-like C++ macro. The I/O segments are specified one-by-one, each as a statement that calls the macro. For example:

void InputFormat() {
    LINE(N, M);
    EMPTY_LINE();
    LINE(A % SIZE(N));
}

Supported I/O segments​

The list of supported segments is given below. In all segments, it must be noted that:

There are two categories of I/O segments: raw segments and tokenized segments.

Raw segments​

These segments do not do any special formatting to the value of the variables; they will print/parse them as-is.

  • Empty line

    Specified by the macro EMPTY_LINE(). Represents a single, empty line.

  • Raw line

    Specified by the macro RAW_LINE(...). Represent a line of the string given as the only argument. The argument must be of std::string type.

    For example: "... the next line consists of a sentence containing arbitrary printable ASCII characters S" can be specified by RAW_LINE(S) (where S is a string).

  • Multiple raw lines

    Specified by the macro RAW_LINES(...) % SIZE(<size>). Represent lines of string given as the only argument. The argument must be of std::vector<std::string> type.

    For example: "... each of the next N lines consists of a sentence containing arbitrary printable ASCII characters S" can be specified by RAW_LINES(S) % SIZE(N) (where S is a vector of strings).

    The size can also be omitted, as long as this is the last segment.

Tokenized segments​

These segments do some formatting to the value of the variables. For example, the elements of a vector variable in a line will be printed space-separated.

warning

In tokenized segments, string variables cannot have whitespaces. For example, hello, world! is considered to have two string variables: hello, and world!. Use raw segments if you want to work with strings containing whitespaces.

  • Single line

    Specified by the macro LINE(...). Represents space-separated values in a single line.

    The macro accepts one or more I/O variables as arguments. The value of the variables will be space-separated. For example: "... the first line consists of two space-separated integers N and M" can be specified by LINE(N, M).

    Besides scalars, the arguments can be vectors, too. You need to specify the number of elements using % SIZE(<size>) syntax after each vector. For example: "... the next line consists of N space-separated integers A[0], A[1], ... A[N-1]" can be specified by LINE(A % SIZE(N)). The size can be a constant as well; for example, LINE(B % SIZE(3)).

    You can freely combine scalars and vectors in LINE(); for example, LINE(N, A % SIZE(N), C % SIZE(2)) would represent a line consisting of N A[0] A[1] ... A[N-1] C[0] C[1].

    Lastly, you can specify a vector without fixed size, as long as it is the last argument. For example: "... the input consists an integer X followed by space-separated integers" can be specified by LINE(X, A) (where A is a vector).

  • Multiple lines

    Specified by the macro LINES(...) % SIZE(<size>). Represents multiple lines, each containing an element of a vector given as the argument.

    For example: "... each of the next N lines contains an integer X[i]" can be specified by LINES(X) % SIZE(N).

    There could be more than one vector as well. For example: "... the next N lines each contains space-separated integers X[i] and Y[i]" can be specified by LINES(X, Y) % SIZE(N). If there are multiple vectors, they all must have the same number of elements.

    You also could specify jagged vector as the last argument. This is useful for input format like, "... then M lines follow. Each line begins with a string op. If op is UPDATE, then it is followed by two integers x y. If it is QUERY, then it is followed by a single integer z". This can be specified by LINES(op, data) where op is a vector<string> and data is a vector<vector<int>>. Then, data[i] represents a vector of integers in the i-th line, which can consist of one or two elements.

    Lastly, the size can also be omitted, as long as this is the last segment.

  • Grid

    Specified by the macro GRID(...) % SIZE(<row>, <column>). Represents a grid containing elements of a matrix given as the only argument, laid out in a grid.

    For example: "... each fo the next R lines contain C integers G[i][j]" can be specified by GRID(G) % SIZE(R, C).

    If the matrix is of type char, the elements in each row is not space-separated, otherwise they are space-separated.

For more details, consult the API reference for I/O formats.

BeforeOutputFormat()​

The special BeforeOutputFormat() method, if specified, will be executed right before the produced output is validated against the output format. It is useful when the output format segments depend on the input variables. For example, suppose that the input is a list of commands, each of which is either a query or an update. The output should contain as many lines as the number of update commands present in the input.

You can declare a helper variable, e.g. update_count, and have LINES(answers) % SIZE(update_count) as the output format. Then, compute the value of update_count in the BeforeOutputFormat() method. For example:

int update_count;
vector<int> answers;

void BeforeOutputFormat() {
    // count the number of update queries and assign it to update_count
}

void OutputFormat() {
    LINES(answers) % SIZE(update_count);
}

Multiple output formats​

Sometimes, there are more than one possible output formats. For example: "If there is no valid solution, output a single line containing -1. Otherwise, the first line of the output should contain K, followed by a line containing K space-separated integers representing the answer."

This can be accomplished using OutputFormatX(), where X is the output format number. A test case output is valid if it conforms to at least one of the output formats.

info

As of this version, you can define up to 5 output formats: OutputFormat1() .. OutputFormat5().

The above example could be implemented as follows.

int impossible;

int K;
vector<int> answers;

void OutputFormat1() {
    LINE(impossible);
}

void OutputFormat2() {
    LINE(K);
    LINE(answers % SIZE(K));
}

Notes​

Unfortunately, the following are not supported (yet):

  • Constants in I/O segments

    For example: "... the first line will always consist of the string BEGIN." Everything must be wrapped in variables.

    As a workaround, just create an input variable and initialize it to BEGIN.

  • Complex conditional I/O format that can't be handled by jagged vectors/raw line(s)

    As a workaround, if you have a very complex output format, you can just omit the methods OutputFormat()/OutputFormatX() altogether and your solution's output won't be checked at all for validity.