C Exercises: Count the number of triangles can be fromed from a given array

C Array: Exercise-52 with Solution

Write a program in C to count the number of triangles that can be formed from a given array.

Sample Solution:

C Code:

#include <stdio.h>
#include <stdlib.h>

int compare(const void* one, const void* two) 
{
    return *(int*)one > *(int*)two;
}
int CountNumberOfTriangles (int *arr1, int arr_size) 
{
    int ctrTriangle = 0, i, j, k;
    qsort(arr1, arr_size, sizeof(int), compare);
 
    for(i = 0; i < arr_size-2; ++i) 
	{

        for (j = i+1; j < arr_size; ++j) 
		{
            k = j +1;
            while (k < arr_size && (arr1[i] + arr1[j])> arr1[k]) 
			{
             k++;
            }
            ctrTriangle += k - j - 1;
        }
    }
    return ctrTriangle;
}
int main() 
{
    int arr1[] =  {6, 18, 9, 7, 10};
	int n = sizeof(arr1)/sizeof(arr1[0]);
	int i;
 //------------- print original array ------------------	
	printf("The given array is :  ");
	for(i = 0; i < n; i++)
	{
	printf("%d  ", arr1[i]);
    } 
	printf("\n");
//------------------------------------------------------ 	
    printf("Number of possible triangles can be formed from the array is: %d\n",
           CountNumberOfTriangles(arr1, n));
    return 0;
}

Sample Output:

The given array is :  6  18  9  7  10  
Number of possible triangles can be formed from the array is: 5

Flowchart:

C Programming Code Editor:

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