how to build spiral square matrix using recursion?

Question

I wanted to build a spiral square matrix using recursion. I am able to build spiral square matrix using iterative method as below:

void main() 
{ 

    int i         


        

Answer 1

#include <stdio.h>

void build_matrix(int msize, int a[msize][msize], int size, int value){
    int i, row, col;
    if(size < 1)
        return;
    row = col = (msize - size) / 2;
    if(size==1){
        a[row][col] = value;
        return;
    }
    for(i=0;i<size-1;++i)
        a[row][col++] = value++;//RIGHT
    for(i=0;i<size-1;++i)
        a[row++][col] = value++;//DOWN
    for(i=0;i<size-1;++i)
        a[row][col--] = value++;//LEFT
    for(i=0;i<size-1;++i)
        a[row--][col] = value++;//UP
    build_matrix(msize, a, size-2, value);
}

int main(){
    int size;
    printf("input size : ");
    scanf("%d", &size);
    int a[size][size];
    build_matrix(size, a, size, 1);
    for(int r=0;r<size;++r){
        for(int c=0;c<size;++c)
            printf("%3d ", a[r][c]);
        printf("\n");
    }

    return 0;
}

Answer 2

Working Code, without divide and Just recurse:

#include <stdio.h>
#include <stdlib.h>
#include <stdbool.h>
#define N 20

bool s[N][N] = {0};
int counter;
typedef enum {
    right = 0,
    down,
    left,
    up
}c_flag;

c_flag flag;
int build_matrix(int a[N][N],int i,int j, c_flag flag)
{
    int ret;
    if (i < 0 || i>=N || j < 0 || j >= N || s[i][j] == true)
        return false;

    if(s[i][j] == false && a[i][j] == 0)
    {
        s[i][j] = true;
        a[i][j] = ++ counter;
    }
    if (flag == right)
        ret = build_matrix(a,i,j+1,right);
    flag = down;

    if (flag == down)
        ret =build_matrix(a,i+1,j,down);
    flag = left;

    if (flag == left)
        ret = build_matrix(a,i,j-1,left);
    flag = up;

    if (flag == up)
        ret = build_matrix (a,i-1,j,up);
    flag = right;

    if (flag == right)
        ret = build_matrix(a,i,j+1,right);
    return false;
}

int main()
{
    int i, j;
    int k, ret;
    //printf("Enter N to construct square matrix \n");
    //scanf("%d",&n);
    int a[N][N] = {0};
    k = N/2 + N%2;
    build_matrix(a,i,i,right);
    for(i = 0; i < N; i++)
    {
        for(j = 0; j < N; j++)
        {
            if (!(a[i][j] < 100))
                printf("%3d ",a[i][j]);
            else if(a[i][j] < 10)
                printf("00%d ",a[i][j]);
            else
                printf("0%d ",a[i][j]);
        }
        printf("\n");
    }
    return 0;
}