The idea and code is just taken from . There is a nice explanation to the code on the answer by BrianLuong1337.

1 class Solution { 2 public: 3     int findPeakElement(vector
     
      & nums) { 4         int n = nums.size(), l = 0, r = n - 1; 5         while (l < r) { 6             int m = (l & r) + ((l ^ r) >> 1), mr = m + 1; 7             if (nums[m] > nums[mr]) r = m; 8             else l = mr; 9         }10         return l;11     }12 };