Suppose we have to find the peak element in an array. The peak element is an element that is greater than its neighbors. Suppose we have an input array nums, where nums[i] ≠ nums[i+1], search for a peak element and return its index. The array can hold multiple peak elements, in that case return the index to any one of the peak elements. We can imagine that nums[-1] = nums[n] = -∞. So if the array is like [1,2,1,3,5,6,4], the peak elements should be 1 or 5.
To solve this, we will follow these steps −
low := 0 and high := last index of array, n := size of array, ans := infinity
while low <= high
mid := low + (high - low)/2
if mid - 1 >= 0 and nums[mid - 1] <= nums[mid], then low := mid, otherwise high := mid - 1
Let us see the following implementation to get better understanding −
class Solution(object): def findPeakElement(self, nums): """ :type nums: List[int] :rtype: int """ low = 0 high = len(nums)-1 while low<high: mid = low + (high - low+1)//2 print(mid) if (mid-1>=0 and nums[mid-1]<=nums[mid]): low = mid else: high = mid-1 return low