数组中的最大值，至少是其他元素的两倍

给定一个长度为n的整数数组。我们的任务是返回max元素的索引，如果它的索引至少是数组中其他每个数字的两倍。如果max元素不满足条件，则返回-1。
例子：

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.

方法：遍历数组以找到唯一的最大元素m ，并跟踪其索引maxIndex 。再次扫描阵列。如果找到m <2 * x的x！= m ，则应返回-1 。否则，我们应该返回maxIndex 。

C++

// CPP program for Maximum of
// the array which is at least
// twice of other elements of
// the array.
#include
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

Java

// 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));
    }
}

Python3

# 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

C#

// 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

 $arr[$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.
?>

Javascript

    // 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.

输出：

1

时间复杂度： $O(n)$