747. Largest Number At Least Twice of Others

Problem

You are given an integer array nums where the largest integer is unique.

Determine 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, or return -1 otherwise.

Example 1:

Input: nums = [3,6,1,0]
Output: 1
Explanation: 6 is the largest integer.
For every other number in the array x, 6 is at least 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 is less than twice the value of 3, so we return -1.

Example 3:

Input: nums = [1]
Output: 0
Explanation: 1 is trivially at least twice the value as any other number because there are no other numbers.

Constraints:

• 1 <= nums.length <= 50
• 0 <= nums[i] <= 100
• The largest element in nums is unique.

Problem Summary

You are given an integer array nums, in which there is always a unique largest integer. Find the largest element in the array and check whether it is at least twice every other number in the array. If it is, return the index of the largest element; otherwise, return -1.

Solution Approach

• Easy problem. First scan once to find the maximum value and its index. Then scan again to check whether the maximum value is twice every other number.

Code

package leetcode

func dominantIndex(nums []int) int {
	maxNum, flag, index := 0, false, 0
	for i, v := range nums {
		if v > maxNum {
			maxNum = v
			index = i
		}
	}
	for _, v := range nums {
		if v != maxNum && 2*v > maxNum {
			flag = true
		}
	}
	if flag {
		return -1
	}
	return index
}