162. Find Peak Element

A peak element is an element that is greater than its neighbors.

Given an input array where 

num[i] ≠ num[i+1]

, find a peak element and return
its index.

The array may contain multiple peaks, in that case return the index to any one of the peaks is fine.

You may imagine that 

num[-1] = num
= -∞

.

For example, in array 

[1, 2, 3, 1]

, 3 is a peak element and your function
should return the index number 2.

题意：找到数组的一个峰值。

思路：二分，mid值以及mid+1，如果mid值大于mid+1，则搜索范围变为(left, mid)，如果mid值小于mid+1,搜索范围变为(mid+1, right)。

class Solution {
public:
int findPeakElement(vector<int>& nums) {
int left = 0;
int right = nums.size() - 1;
while (left < right){
int mid = (left + right) / 2;
int mid2 = mid + 1;
if (nums[mid] > nums[mid2]){
right = mid;
}
else{
left = mid2;
}
}
return left;
}
};