Java Array Exercises: Count the number of possible triangles from a given unsorted array of positive integers

Java Array: Exercise-44 with Solution

Write a Java program to count the number of possible triangles from a given unsorted array of positive integers.

Note: The triangle inequality states that the sum of the lengths of any two sides of a triangle must be greater than or equal to the length of the third side.

Sample Solution:

Java Code:

import java.util.*;
import java.lang.*;
public class Main
{
   public static void main (String[] args) 
    {  
        int nums[] = {6, 7, 9, 16, 25, 12, 30, 40};
        int n = nums.length;
        System.out.println("Original Array : "+Arrays.toString(nums));  

        // Sort the array elements in non-decreasing order
        Arrays.sort(nums);
        
        // Initialize count of triangles
        int ctr = 0;
 
        for (int i = 0; i < n-2; ++i)
        {
          int x = i + 2;
 
          for (int j = i+1; j < n; ++j)
            {
               while (x < n && nums[i] + nums[j] > nums[x])
               ++x;
                 ctr += x - j - 1;
            }
        }
    System.out.println("Total number of triangles:  " +ctr);
    }
}

Sample Output:

                                                                              
Original Array : [6, 7, 9, 16, 25, 12, 30, 40]
Total number of triangles:  17

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