747. Largest Number Greater Than Twice of Others

　　　　这道题为简单题

题目:　　　　　　　　　

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.

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.

Note:

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

思路：

　　　　这个题比较简单，用两个变量跟踪整个列表中的最大和次大值的索引，最后比较即可。

代码：

 1 class Solution(object):
 2     def dominantIndex(self, nums):
 3         """
 4         :type nums: List[int]
 5         :rtype: int
 6         """
 7         
 8         
 9         max_index = 0
10         min_index = float(‘-inf‘)
11         if len(nums) < 2:
12             return max_index
13         
14         for i in range(1, len(nums)):
15             if nums[i] > nums[max_index]:
16                 min_index = max_index
17                 max_index = i
18             elif (nums[i] < nums[max_index]) and (min_index == float(‘-inf‘) or nums[i] > nums[min_index]):
19                 min_index = i;
20         
21         if nums[max_index] >= nums[min_index] * 2: return max_index
22         else: return -1