Leaders in an array

1.6

Write a program to print all the LEADERS in the array. An element is leader if it is greater than all the elements to its right side. And the rightmost element is always a leader. For example int the array {16, 17, 4, 3, 5, 2}, leaders are 17, 5 and 2.

Let the input array be arr[] and size of the array be size.

Method 1 (Simple)
Use two loops. The outer loop runs from 0 to size – 1 and one by one picks all elements from left to right. The inner loop compares the picked element to all the elements to its right side. If the picked element is greater than all the elements to its right side, then the picked element is the leader.

C++

#include<iostream>
using namespace std;

/*C++ Function to print leaders in an array */
void printLeaders(int arr[], int size)
{
    for (int i = 0; i < size; i++)
    {
        int j;
        for (j = i+1; j < size; j++)
        {
            if (arr[i] <= arr[j])
                break;
        }    
        if (j == size) // the loop didn't break
            cout << arr[i] << " ";
  }
}

/* Driver program to test above function */
int main()
{
    int arr[] = {16, 17, 4, 3, 5, 2};
    int n = sizeof(arr)/sizeof(arr[0]);
    printLeaders(arr, n);
    return 0;
}

Java

class LeadersInArray 
{
    /*Java Function to print leaders in an array */
    void printLeaders(int arr[], int size) 
    {
        for (int i = 0; i < size; i++) 
        {
            int j;
            for (j = i + 1; j < size; j++) 
            {
                if (arr[i] <= arr[j])
                    break;
            }
            if (j == size) // the loop didn't break
                System.out.print(arr[i] + " ");
        }
    }

    /* Driver program to test above functions */
    public static void main(String[] args) 
    {
        LeadersInArray lead = new LeadersInArray();
        int arr[] = new int[]{16, 17, 4, 3, 5, 2};
        int n = arr.length;
        lead.printLeaders(arr, n);
    }
}

Python

# Python Function to print leaders in array

def printLeaders(arr,size):
    
    for i in range(0, size):
        for j in range(i+1, size):
            if arr[i]<=arr[j]:
                break
        if j == size-1: # If loop didn't break
            print arr[i],

# Driver function
arr=[16, 17, 4, 3, 5, 2]
printLeaders(arr, len(arr))

# This code is contributed by _Devesh Agrawal__


Output:
17 5 2

Time Complexity: O(n*n)



Method 2 (Scan from right)
Scan all the elements from right to left in array and keep track of maximum till now. When maximum changes it’s value, print it.

C++

#include <iostream>
using namespace std;

/* C++ Function to print leaders in an array */
void printLeaders(int arr[], int size)
{
    int max_from_right =  arr[size-1];

    /* Rightmost element is always leader */
    cout << max_from_right << " ";
    
    for (int i = size-2; i >= 0; i--)
    {
        if (max_from_right < arr[i])
        {           
            max_from_right = arr[i];
            cout << max_from_right << " ";
        }
    }    
}

/* Driver program to test above function*/
int main()
{
    int arr[] = {16, 17, 4, 3, 5, 2};
    int n = sizeof(arr)/sizeof(arr[0]);
    printLeaders(arr, n);
    return 0;
}    

Java

class LeadersInArray 
{
    /* Java Function to print leaders in an array */
    void printLeaders(int arr[], int size)
    {
        int max_from_right =  arr[size-1];
 
        /* Rightmost element is always leader */
        System.out.print(max_from_right + " ");
     
        for (int i = size-2; i >= 0; i--)
        {
            if (max_from_right < arr[i])
            {           
            max_from_right = arr[i];
            System.out.print(max_from_right + " ");
            }
        }    
    }

    /* Driver program to test above functions */
    public static void main(String[] args) 
    {
        LeadersInArray lead = new LeadersInArray();
        int arr[] = new int[]{16, 17, 4, 3, 5, 2};
        int n = arr.length;
        lead.printLeaders(arr, n);
    }
}

Python

# Python function to print leaders in array
def printLeaders(arr, size):
   
    max_from_right = arr[size-1]   
    print max_from_right,    
    for i in range( size-2, 0, -1):        
        if max_from_right < arr[i]:            
            print arr[i],
            max_from_right = arr[i]
        
# Driver function
arr = [16, 17, 4, 3, 5, 2]
printLeaders(arr, len(arr))

# This code contributed by _Devesh Agrawal__


Output
2 5 17


Time Complexity:
O(n)

Asked in: Payu

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