How to find all leaders in an array in Java?

In Java, Array is an object. It is a non-primitive data type which stores values of similar data type.

As per the problem statement we have to find leaders in an array. An element is a leader if it is greater than all the elements to its right side.

Let’s start!

To Show You Some Instances

Instance-1

Suppose the original array is {16, 17, 4, 3, 11, 14, 23, 2, 6, 10}.

After finding leaders in an array the result will be − 23 10

Instance-2

Suppose the original array is {16, 17, 4, 3, 5, 6, 9, 1, 8, 2}.

After finding leaders in an array the result will be − 17 9 8 2

Instance-3

Suppose the original array is {1, 5, 7, 3, 2, 1}

After finding leaders in an array the result will be − 7 1

Algorithm-1: (Brute Force Approach)

• Step 1 − Declare and initialize an integer array.

• Step 2 − Initialize two for loop one inside another.

• Step 3 − Take one element from the first element from the outer for loop.

• Step 4 − Compare the element with its next elements by using an inner for loop.

• Step 5 − If the outer for loop element remains greater till the last element of the array, then print that element.

• Step 6 − Finally, you will get all the leaders printed in the console.

Algorithm-2: (Optimized Approach)

• Step 1 − Declare and initialize an integer array.

• Step 2 − Take for loop and start iterating the array from the rightmost element and track the max.

• Step 3 − Anytime you get any new max element then the previous max element is a leader.

• Step 4 − Finally, you will get all the leaders printed in the console.

Multiple Approaches

We have provided the solution in different approaches.

• By Using Brute Force Approach (Left to Right Element Scan)

• By Using Brute Force Approach with User Defined Method

• By Using Optimized Approach (Right to Left Element Scan)

Let’s see the program along with its output one by one.

Approach-1: By Using Brute Force Approach

Example

We will solve this program by using Algorithm-1.

public class Main{
   public static void main(String[] args){
   
      //Declare and initialize the array elements
      int array[] = {16, 17, 4, 3, 5, 6, 9, 1, 8, 2};
      int size = array.length;
      System.out.println("Leaders in the array are: ");

      //Logic Implementtaion
      for (int i = 0; i < size; i++){
         int j;
         for (j = i + 1; j < size; j++){
            if (array[i] <=array[j])
               break;
         }
         if (j == size) // the loop didn't break{
         
            //print the result
            System.out.print(array[i] + " ");
         }
      }
   }

Output

Leaders in the array are: 
17 9 8 2

Approach-2: By Using Brute Force Approach with User Defined Method

Example

We will solve this program by using Algorithm-1 but here we will make use of a user defined method.

public class Main{
   public static void main(String[] args){
   
      //Declare and initialize the array elements
      int array[] = {16, 17, 4, 3, 5, 6, 9, 1, 8, 2};
      int m = array.length;
      System.out.println("Leaders in the array are: ");
      
      //call a user defined method
      findLeaders(array, m);
   }
   
   //main method
   static void findLeaders(int array[], int size){
   
      //Logic Implementtaion
      for (int i = 0; i < size; i++){
         int j;
         for (j = i + 1; j < size; j++){
            if (array[i] <=array[j])
               break;
         }
         if (j == size) // the loop didn't break{
         
            //print the result
            System.out.print(array[i] + " ");
         }
      }
   }

Output

Leaders in the array are: 
17 9 8 2

Approach-3: By Using Optimized Approach

Example

We will solve this program by using Algorithm-2

public class Main{
   public static void main(String[] args){
   
      //Declare and initialize the array elements
      int array[] = {16, 17, 4, 3, 5, 6, 9, 1, 8, 2};
      int m = array.length;
      System.out.println("Leaders in the array are: ");
      
      //call a user defined method
      findLeaders(array, m);
   }
   
   //main method
   static void findLeaders(int arr[], int size){
   
      //Logic Implementtaion
      int rightMaximum=arr[arr.length-1];
      
      //Here we have started loop from size-2 
      
      //as rightmost element is always a leader
      System.out.print(rightMaximum+" ");
      for (int i = size-2; i>=0; i--) {
         if(arr[i] > rightMaximum){
            rightMaximum=arr[i];
            System.out.print(rightMaximum+" ");
         }
      }
   }
}

Output

Leaders in the array are: 
2 8 9 17

In this article, we explored how to find leaders in an array by using Java.