747. Largest Number At Least Twice of Others

1. Description

In a given integer array nums, there is always exactly one largest element.
Find whether the largest element in the array is at least twice as much as every other number in the array.
If it is, return the index of the largest element, otherwise return -1.

2. Example

Example 1:
Input: nums = [3, 6, 1, 0]
Output: 1
Explanation: 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.

Example 2:
Input: nums = [1, 2, 3, 4]
Output: -1
Explanation: 4 isn’t at least as big as twice the value of 3, so we return -1.

3. Note

• nums will have a length in the range [1, 50].
• Every nums[i] will be an integer in the range [0, 99].

4. Solutions

My Accepted Solution

n = i_nums.size()
Time complexity: O(n)
Space complexity: O(1)

class Solution 
{
public:
    // int dominantIndex(vector<int>& nums) 
    int dominantIndex(vector<int> &i_nums) 
    {
        int maxValueIndex = max_element(i_nums.begin(), i_nums.end()) - i_nums.begin();
        
        for(int i = 0; i < i_nums.size(); i++)
        {
            if(i != maxValueIndex && i_nums[i] * 2 > i_nums[maxValueIndex])
                return -1;
        }
        
        return maxValueIndex;
    }
};