CODEWITHSUNDEEP
algorithmdata-structures
Anup Buchke
Anup Buchke

Reputation: 5520

Efficient method for generating these sequence

Problem: I need to generate the following sequence. I have the order of the matrix as input.

Example:
I need to generate the sequence of position of its elements.

 (0,0),(0,1),(1,0),(1,1) ->for order 2
 (0,0),(0,1),(0,2),(1,0),(1,1),(1,2),(2,0),(2,1),(2,2) -> for order 3.

I need to have function which does this for me. When I call this function it should calculate for me on the fly. I don't want to store the sequence in the memory.

Eg: 

first_call - > return value (0,0)
second_call to function - > return value ( 0,1)
...and so on...

You can store these values in some global variables.

PS:
The function has to be thread-safe as the application is multi-threaded. I know this condition doesn't make difference. Just wanted to convey the entire problem.

Precision:
I have tried my solution but I think its in efficient. I am looking for an efficient method to do that. You can just mention the steps. I don't need implementation in any particular language. Please let me know if more info is required for the question.

Upvotes: 2

Views: 104

Answers (3)

Paddy3118
Paddy3118

Reputation: 4772

Here's a Python solution using a generator:

def sequence_gen(order=2):
    for i in range(order*order):
        yield divmod(i, order)


for val in sequence_gen(2):
    print(val)

#(0, 0)
#(0, 1)
#(1, 0)
#(1, 1)

for val in sequence_gen(3):
    print(val)

#(0, 0)
#(0, 1)
#(0, 2)
#(1, 0)
#(1, 1)
#(1, 2)
#(2, 0)
#(2, 1)
#(2, 2)

Upvotes: 0

James
James

Reputation: 9278

#define MATRIX_ORDER 3

void NextPosition(int aIndex, int& aRow, int& aColumn)
{
    if (aColumn == MATRIX_ORDER - 1)
    {
        aRow++;
        aColumn = 0;
    } else {
        aColumn++;
    }
}


void SomeFunction()
{
    int index = 0;
    int row = 0;
    int column = -1;

    while (index < (MATRIX_ORDER * MATRIX_ORDER))
    {
        NextPosition(index, row, column);
        printf("index: %d, row: %d, column: %d\n", index, row, column);
        index++;
    }
}

Output:

index: 0, row: 0, column: 0
index: 1, row: 0, column: 1
index: 2, row: 0, column: 2
index: 3, row: 1, column: 0
index: 4, row: 1, column: 1
index: 5, row: 1, column: 2
index: 6, row: 2, column: 0
index: 7, row: 2, column: 1
index: 8, row: 2, column: 2

Upvotes: 0

mprivat
mprivat

Reputation: 21902

Use a global variable to store the number of times you have called the function. Call it t. If order is order, then

f = (t div order, t mod order)

Where div is the integer division (e.g. 5 div 3 = 1) and mod is the modulus (i.e. remainder of the division). (e.g. 5 mod 3 = 2).

So in Java for example:

public class MyCounter {

    private static int t = 0;

    public static int[] myFunction(int order) {
        return new int[] { t / order , t++ % order };
    }

    public static void main(String[] args) {
        int order = 3;
        for(int i=0; i<order*order; i++) {
            int[] k = myFunction(order);            
            System.out.println("("+k[0]+", "+k[1]+")");
        }
    }
}

Upvotes: 2

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