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

09 Apr, 2021
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++
Java
Python3
C#
PHP
Javascript
// CPP program for Maximum of// the array which is at least// twice of other elements of// the array.#include<bits/stdc++.h>using namespace std;     // Function to find the// index of Max element// that satisfies the// conditionint 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 functionint 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
// 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));    }}
# 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 conditiondef 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 codearr = [3, 6, 1, 0]print(findIndex(arr)) # This code is contributed by Smitha Dinesh Semwal
// 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.
<?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// conditionfunction 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.?>
<script>    // Javascript 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        let maxIndex = 0;        for (let 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 (let i = 0; i < len; ++i)                        if (maxIndex != i &&                arr[maxIndex] < 2 * arr[i])                return -1;         return maxIndex;    }         let arr = [3, 6, 1, 0];    let len = arr.length;           document.write(findIndex(arr, len));         // This code is contributed by divyeshrabadiya07.</script>
Output:  
1
Time Complexity:  
vt_m
divyeshrabadiya07
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