Exercise 5: Find the Peak Element

Your Task

A peak element is an element that is strictly greater than its neighbours.

Write a function find_peak(nums) that returns the index of any peak element in nums.

• You may assume nums[-1] and nums[n] are treated as -∞ (negative infinity).
• There is always at least one peak.
• Your solution must run in O(log n).

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Examples

print(find_peak([1, 2, 3, 1]))      # 2  (nums[2] = 3 is a peak)
print(find_peak([1, 2, 1, 3, 5]))   # 1 or 4  (either is valid)
print(find_peak([1]))               # 0
print(find_peak([3, 2, 1]))         # 0  (nums[0] = 3 is a peak)
print(find_peak([1, 2, 3]))         # 2  (nums[2] = 3 is a peak)

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Expected Complexity

	Complexity
Time	O(log n) — binary search
Space	O(1)

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Starter Code

def find_peak(nums):
    pass

print(find_peak([1, 2, 3, 1]))      # 2
print(find_peak([1, 2, 1, 3, 5]))   # 1 or 4
print(find_peak([1]))               # 0
print(find_peak([3, 2, 1]))         # 0
print(find_peak([1, 2, 3]))         # 2

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Hints