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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

Flowchart:

Flowchart: Count the number of possible triangles from a given unsorted array of positive integers

Visualize Java code execution (Python Tutor):


Java Code Editor:

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Java: Tips of the Day

Different between parseInt() and valueOf() in java?

Well, the API for Integer.valueOf(String) does indeed say that the String is interpreted exactly as if it were given to Integer.parseInt(String). However, valueOf(String) returns a new Integer() object whereas parseInt(String) returns a primitive int.

If you want to enjoy the potential caching benefits of Integer.valueOf(int), you could also use this eyesore:

Integer k = Integer.valueOf(Integer.parseInt("123"))

Now, if what you want is the object and not the primitive, then using valueOf(String) may be more attractive than making a new object out of parseInt(String) because the former is consistently present across Integer, Long, Double, etc.

Ref: https://bit.ly/3vRuIPY