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