Maximum in array which is at-least twice of other elements

Given an array of integers of length n. Our task is to return the index of the max element if the it is at least twice as much as every other number in the array. If the max element does not satisfy the condition return -1.

Examples:

Input : arr = {3, 6, 1, 0}
Output : 1
Here, 6 is the largest integer, and for 
every other number in the array x, 6 is 
more than twice as big as x. The index of
value 6 is 1, so we return 1.

Input : arr = {1, 2, 3, 4}
Output : -1
4 isn't at least as big as twice the value
of 3, so we return -1.



Approach : Scan through the array to find the unique largest element m, keeping track of it’s index maxIndex. Scan through the array again. If we find some x != m with m < 2*x, we should return -1. Otherwise, we should return maxIndex.

C++

filter_none

edit
close

play_arrow

link
brightness_4
code

// CPP program for Maximum of
// the array which is at least
// twice of other elements of
// the array.
#include<iostream>
using namespace std;
      
// Function to find the 
// index of Max element 
// that satisfies the 
// condition
int findIndex(int arr[], int len) { 
      
    // Finding index of
    // max of the array
    int maxIndex = 0;
    for (int i = 0; i < len; ++i) 
        if (arr[i] > arr[maxIndex])
            maxIndex = i;
      
    // Returns -1 if the
    // max element is not 
    // twice of the i-th
    // element. 
    for (int i = 0; i < len; ++i)             
        if (maxIndex != i &&
            arr[maxIndex] < 2 * arr[i])
            return -1;
      
    return maxIndex;
}
      
// Driver function
int main(){
    int arr[] = {3, 6, 1, 0};
    int len = sizeof(arr) / sizeof(arr[0]);
      
    cout<<(findIndex(arr, len));
}
  
// This code is contributed by Smitha Dinesh Semwal

chevron_right


Java

filter_none

edit
close

play_arrow

link
brightness_4
code

// Java program for Maximum of the array
// which is at least twice of other elements 
// of the array.
import java.util.*;
import java.lang.*;
  
class GfG {
      
    // Function to find the index of Max element
    // that satisfies the condition
    public static int findIndex(int[] arr) {        
          
        // Finding index of max of the array
        int maxIndex = 0;
        for (int i = 0; i < arr.length; ++i) 
            if (arr[i] > arr[maxIndex])
                maxIndex = i;
          
        // Returns -1 if the max element is not 
        // twice of the i-th element.        
        for (int i = 0; i < arr.length; ++i)             
            if (maxIndex != i && arr[maxIndex] < 2 * arr[i])
                return -1;
          
        return maxIndex;
    }
      
    // Driver function
    public static void main(String argc[]){
        int[] arr = new int[]{3, 6, 1, 0};
        System.out.println(findIndex(arr));
    }
}

chevron_right


Python3

filter_none

edit
close

play_arrow

link
brightness_4
code

# Python 3 program for Maximum of 
# the array which is at least twice  
# of other elements of the array.
  
# Function to find the index of Max 
# element that satisfies the condition
def findIndex(arr): 
          
    # Finding index of max of the array
    maxIndex = 0
    for i in range(0,len(arr)):
        if (arr[i] > arr[maxIndex]):
            maxIndex = i
      
    # Returns -1 if the max element is not 
    # twice of the i-th element.     
    for i in range(0,len(arr)):     
        if (maxIndex != i and 
                arr[maxIndex] < (2 * arr[i])):
            return -1
          
    return maxIndex
      
      
# Driver code
arr = [3, 6, 1, 0]
print(findIndex(arr))
  
# This code is contributed by Smitha Dinesh Semwal

chevron_right


C#

filter_none

edit
close

play_arrow

link
brightness_4
code

// C# program for Maximum of the array
// which is at least twice of other elements 
// of the array.
using System;
  
class GfG {
      
    // Function to find the index of Max element
    // that satisfies the condition
    public static int findIndex(int[] arr) {     
          
        // Finding index of max of the array
        int maxIndex = 0;
        for (int i = 0; i < arr.Length; ++i) 
            if (arr[i] > arr[maxIndex])
                maxIndex = i;
          
        // Returns -1 if the max element is not 
        // twice of the i-th element. 
        for (int i = 0; i < arr.Length; ++i)         
            if (maxIndex != i && arr[maxIndex] < 2 * arr[i])
                return -1;
          
        return maxIndex;
    }
      
    // Driver function
    public static void Main()
    {
        int[] arr = new int[]{3, 6, 1, 0};
        Console.WriteLine(findIndex(arr));
    }
}
  
// This code is contributed by vt_m.

chevron_right


PHP

filter_none

edit
close

play_arrow

link
brightness_4
code

<?php
// PHP program for Maximum of
// the array which is at least
// twice of other elements of
// the array.
  
// Function to find the 
// index of Max element 
// that satisfies the 
// condition
function findIndex($arr, $len
      
    // Finding index of
    // max of the array
    $maxIndex = 0;
    for ( $i = 0; $i < $len; ++$i
        if ($arr[$i] > $arr[$maxIndex])
            $maxIndex = $i;
      
    // Returns -1 if the
    // max element is not 
    // twice of the i-th
    // element. 
    for ($i = 0; $i < $len; ++$i)             
        if ($maxIndex != $i and
            $arr[$maxIndex] < 2 * $arr[$i])
            return -1;
      
    return $maxIndex;
}
      
// Driver Code
$arr = array(3, 6, 1, 0);
$len = count($arr);
  
echo findIndex($arr, $len);
  
// This code is contributed by anuj_67.
?>

chevron_right



Output:

1

Time Complexity:  O(n)



My Personal Notes arrow_drop_up

Intern at GeeksforGeeks

If you like GeeksforGeeks and would like to contribute, you can also write an article using contribute.geeksforgeeks.org or mail your article to contribute@geeksforgeeks.org. See your article appearing on the GeeksforGeeks main page and help other Geeks.

Please Improve this article if you find anything incorrect by clicking on the "Improve Article" button below.



Improved By : vt_m



Article Tags :
Practice Tags :


1


Please write to us at contribute@geeksforgeeks.org to report any issue with the above content.