Python descriptor details

OJ IO

The motivation of this blog is learning the method of implementation of input and output of OJ mode. Because I used to practice programming in LeetCode, it is very verdant for me to program in the NowCoder. In the light of this, several common IO situations of OJ mode will be discussed here, as well as an practical example.

In conclusion, input data will be written in line by line from stdin in terms of OJ mode. Particularly, the different types of data will be taken into account with respect to C language.

Int

1. Multiple sets of input data without a specific limitation of quantity. Write data until the end of input file.

int main()
{
    int m;
    while( scanf("%d", &m) != EOF )
        ...
}

Here, EOF is a defined macro with value of -1. The return value will be the total number of characters written successfully. Otherwise, it will be a negative value. Therefore, the while loop is intended to write data from stdin continuously(line by line) until the end of the file.

In addition, due to the value of EOF(i.e. -1), the code can be simplified as below:

int main()
{
    int m;
    while( ~scanf("%d", &m) )
        ...
}

Because of ~-1=0, above code is the other form of aforementioned write method.

2. Multiple sets of input data without a specific limitation of quantity. Write data until the end of input file. But a special symbol is used as the ending sign.

int main()
{
    int m;
    while( scanf("%d", &m) != EOF && m != 0) // == while( ~scanf("%d", &m) && m != 0)
        ...
}

//input data example:
// 3
// 10
// 81
// 0  // the end of sign, we should not deal with this line.

3. Given a specific N multiple sets of input data, then write data these N sets of data.

int main()
{
    int N;
    int a,b;
    scanf("%d", &N);
    while(N--)
    {
        scanf("%d %d", &a, &b);
        ...
    }
}

This is the most common situation in fact, the practical example is on the basis of this situation.

String

1. No Whitespace(), Newline(\n), Carriage Return(\r), and Tab(\t) at each String.

// input: 
// abc def

char s1[100], s2[100];
scanf("%s %s", s1, s2);

2. No Newline(\n) or Carriage Return(\r) at each String.

// input: 
// Hello World!

char s1[100];
gets(s1);

gets() function will be used to write the String in terms of this situation. Because we are facing a training environment, the length of input will be guaranteed. Therefore, the risk of gets function can be ignored. We can also use fgets() to assign a specific length of String will be write. Additionally, the return value of NULL means the end of file or error generated.

Note that using scanf before gets may cause an unexpected problem, click here to check the detail.

An example

In this case, we will read 3 sets of data, each set contains one line(2 integers) to describe the value of rows and cols. Then are values of a matrix with rows row and cols columns.

// input:
// 3              // There are 3 datasets in total
// 5 10           // There are 5 rows and 10 columns in the first dataset
// AAAAAADROW
// WORDBBBBBB
// OCCCWCCCCC
// RFFFFOFFFF
// DHHHHHRHHH
// WORD           // The target word of the first dataset
// 3 3            // There are 3 rows and 3 columns in the second dataset
// AAA
// AAA
// AAA
// AA             // The target word of the second dataset
// 5 8            // There are 5 rows and 8 columns in the third dataset
// WORDSWOR
// ORDSWORD
// RDSWORDS
// DSWORDSW
// SWORDSWO
// SWORD          // The target word of the third dataset

void input(int *rows, int *cols, char *target, char **matrix){
    scanf("%d %d\n", rows, cols); // MUST ADD '\n'!!
    for(int i=0; i<*rows; i++)
    {
        matrix[i] = (char *)malloc(*cols * sizeof(char));
        gets(matrix[i]);
    }
    gets(target);
}

int main(int argc, char* argv[]){
    int N;
    scanf("%d\n", &N); // MUST ADD '\n'!!
    int count = 0;
    int rows, cols;
    char *target = (char *)malloc(9 * sizeof(char));
    char **matrix = (char **)malloc(99 * sizeof(char *));
    for(int i=0; i<99; i++)
        matrix[i] = (char *)malloc( 99 * sizeof(char));
    while(N--)
    {
        input(&rows, &cols, target, matrix);
    }
    return 0;
}

An important note here is that if we read integer by scanf firstly, and then read String by gets, we must add the \n in the scanf function. Because the scanf("%d\n", &N); will stop writing once finishing the integer written. Therefore, the last new-line character will not be consumed by scanf.

References:

• OJ IO
• ~scanf
• Newline and Return
• scanf not deal with new-line character

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