number_triangle_pattern_alternate.c

/*

    number_triangle_pattern_alternate.c

https://www.facebook.com/groups/3092811364081112/permalink/7605244639504406/

Solution from Dan Mathew Gamale :
https://www.facebook.com/groups/3092811364081112/user/100005184546962/

numbers           indexes           matrix

1                 00                00 01 02 03 04
2 9               10 11             10 11 12 13 14
3 8 10            20 21 22          20 21 22 23 24
4 7 11 14         30 31 32 33       30 31 32 33 34
5 6 12 13 15      40 41 42 43 44    40 41 42 43 44


    You can find all my C programs at Dragan Milicev's pastebin:

    https://pastebin.com/u/dmilicev

*/

#include<stdio.h>
#include <string.h>                 // for memset()

// print triangle of numbers
void number_triangle_pattern_from_top(int n){
    int r,c, num=1;                 // r - row, c - column, num - number
    int arr[n][n];                  // n - number of rows and columns

    // memset() is used to fill a block of memory with a particular value.
    memset(arr,0,sizeof(arr));      // set all elements to 0

/*
    for(r=0; r<n; r++)              // set all elements to 0, another way
        for(c=0; c<n; c++)
            arr[r][c]=0;
*/
    // set all elements to num
    for(c=0; c<n; c++)              // column
        for (r=0; r<n-c; r++)       // row
            if (c%2)                // odd column
                arr[n-r-1][c] = num++;
            else
                arr[r+c][c] = num++;

    // print triangle
    for(r=0; r<n; r++) {            // row
        for(c=0; c<n; c++)          // column
            if (arr[r][c] != 0)
                printf("%3d",arr[r][c]);
        printf("\n");
    }

    printf("\n");
}


int main(void){
    int n;                          // n - number of rows and columns

    for(n=3; n<=6; n++){            // a few examples
        printf("\n  n = %d \n\n",n);
        number_triangle_pattern_from_top(n);
    }

    return 0;
} // main()