Add the diagonals of an array

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Add the diagonals of an array

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#1 by (2 votes)

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I need to make a program that adds diagonals to an array. According to the example

ButI'mhavingalotoftrouble.Hereisthecode:

#include<stdio.h>#include<math.h>#defineM4#defineN3intmain(){inti,j,soma=0;intmat[M][N]={{1,2,3},{4,5,6},{7,8,9},{10,11,12}},result[M+N-1];for(i=0;i<M+N-1;i++){//deixartodosvaloresdovetoriguaisazeroresult=0;}inta,b,k=0,aux;//auxiliaresfor(i=M-1;i>=0;i--){for(j=N-1;j>=0;j--){result[k]=mat[j];//posição0dovetorrecebeposição4x3damatriz;a=i;b=j;while(a>=0&&b<N&&b>=0){//verificarselinha>=0,coluna<Ne>=0a--;//decrementalinhab++;//acrescentacolunaresult[k]+=mat[a];//valordaposição0dovetorsomacomoproximovalodadiagonalsuperiordireita}k++;//avançaparaproximaposiçãodovetor*/}}for(i=0;i<M;i++){for(j=0;j<N;j++){printf("\t%d   ", mat[j]);
        }
        printf("\n");
    }

    printf("\n");

    for(i=0; i<M+N-1; i++){
        printf("%d   ", result);
    }
}

At first I'm trying to do only the sum of the diagonals and then use the threads to carry out the processes. Can anybody help me? Thank you in advance.

c matriz

asked by anonymous 20.04.2017 / 18:40

1 answer

Arrange a json and write the results It takes time to load RecyclerView

score 2 · Answer 1

Solution only implementing logic of sums, as required, without working with threads .

The logic, as I commented here , to define the secondary diagonals are to check the sum between the position of the line and the column of the element. For example, consider the generic array below:

    [ a00 a01 a02 ]
A = [ a10 a11 a12 ]
    [ a20 a21 a22 ]
    [ a30 a31 a32 ]

Applying the sum of the secondary diagonals, storing the sum in a resultado array, we have:

resultado[0] = a00
resultado[1] = a10 + a01
resultado[2] = a20 + a11 + a02
resultado[3] = a30 + a21 + a12 + a03
resultado[4] = a31 + a22
resultado[5] = a32

Notice that the sum of i and j always results in the position of the resultado array? That is, for resultado[0] the sum i+j is always 0, for resultado[1] the sum i+j is always 1, so in succession. So the code would look something like:

#define M 4
#define N 3
#define Z M+N-1

int main(int argc, char const *argv[]) {

    int mat[M][N] = {
        { 1,  2,  3},
        { 4,  5,  6},
        { 7,  8,  9},
        {10, 11, 12}
    };

    int result[Z] = {0};

    // z varia de 0 a M+N-1, exclusive
    // Indica a linha na matriz resultados:
    for (int z = 0; z < Z; z++) {

        // i varia de 0 a M, exclusive
        // Indica a linha na matriz mat:
        for (int i = 0; i < M; i++) {

            // j varia de 0 a N, exclusive
            // Indica a coluna na matriz mat:
            for (int j = 0; j < N; j++) {

                // Se a soma da posição for igual a z:
                if (i + j == z) {

                    // Incrementa a soma:
                    result[z] += mat[i][j];

                }

            }

        }

        // Exibe o resultado da soma:
        printf("%2d\n", result[z]);

    }

    return 0;
}

When executing the code, the output will be:

Note : The question image has the wrong result in the fourth line, since the sum should be 10+8+6 and 10+9+6 .

To implement logic with threads , instead of you iterating over the value of z , you create the T threads , where each is responsible for calculating a particular result position. You could even define a function to calculate a specific diagonal:

int sum(int z, int mat[M][N]) {

    int result = 0;

    // i varia de 0 a M, exclusive
    // Indica a linha na matriz mat:
    for (int i = 0; i < M; i++) {

        // j varia de 0 a N, exclusive
        // Indica a coluna na matriz mat:
        for (int j = 0; j < N; j++) {

            // Se a soma da posição for igual a z:
            if (i + j == z) {

                // Incrementa a soma:
                result += mat[i][j];

            }

        }

    }

    return result;

}

And make calls of result[0] = sum(0, mat) , result[1] = sum(1, mat) , ..., in threads .

See working at Ideone .