Question

How to count the number of possible triangles from a given array in Java

Answer 1

// Triangle = the sum of any two values (sides) > than the third value (third side)

// A + B > C
// B + C > A
// C + A > B
 
public class MyClass {
    private static int CountTriangles(int[] arr) {
    	int size = arr.length;
    	int count = 0;
    
    	for (int i = 0; i < size; i++) {
    		for (int j = i + 1; j < size; j++) {
    			for (int k = j + 1; k < size; k++) {
    				if (arr[i] + arr[j] > arr[k] && 
    				    arr[i] + arr[k] > arr[j] && 
    				    arr[k] + arr[j] > arr[i]) {
    					count++;
    					System.out.print(arr[i] + " + " + arr[j] + " > " + arr[k] + " | ");
    					System.out.print(arr[i] + " + " + arr[k] + " > " + arr[j] + " | ");
    					System.out.println(arr[k] + " + " + arr[j] + " > " + arr[i]);
    				}
    			}
    		}
    	}
    	return count;
    }
    public static void main(String args[]) {
        int[] arr = {120, 80, 13, 16, 9, 14, 19};


	    int total_triangles = CountTriangles(arr);

	    System.out.print("Total triangles : " + total_triangles);
    }
}






/*
run:
 
13 + 16 > 9 | 13 + 9 > 16 | 9 + 16 > 13
13 + 16 > 14 | 13 + 14 > 16 | 14 + 16 > 13
13 + 16 > 19 | 13 + 19 > 16 | 19 + 16 > 13
13 + 9 > 14 | 13 + 14 > 9 | 14 + 9 > 13
13 + 9 > 19 | 13 + 19 > 9 | 19 + 9 > 13
13 + 14 > 19 | 13 + 19 > 14 | 19 + 14 > 13
16 + 9 > 14 | 16 + 14 > 9 | 14 + 9 > 16
16 + 9 > 19 | 16 + 19 > 9 | 19 + 9 > 16
16 + 14 > 19 | 16 + 19 > 14 | 19 + 14 > 16
9 + 14 > 19 | 9 + 19 > 14 | 19 + 14 > 9
Total triangles : 10
 
*/

 

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