WitnessesMurder.py

'''
Witness of The Tall People

Hi, here's your problem today. This problem was recently asked by Google:

There are n people lined up, and each have a height represented as an integer. A murder has happened right in front of them, and only people who are taller than everyone in front of them are able to see what has happened. How many witnesses are there?

Example:
Input: [3, 6, 3, 4, 1]  
Output: 3
Explanation: Only [6, 4, 1] were able to see in front of them.
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36341                                 x (murder scene)
'''
def witnesses(heights):
    max_height = float('-inf')
    witnesses = 0
    for idx in range(len(heights)-1, -1, -1):
        if heights[idx] > max_height:
            witnesses += 1
            max_height = heights[idx]
    return witnesses

print(witnesses([3, 6, 3, 4, 1]))
# 3
print(witnesses([3, 4, 4, 4, 1]))
# 2
print(witnesses([-1, -3, -7, -2]))
# 2

This is good, but what if all the elements in the list are negative? Or what if there are two elements with the same height? Additionally, reversing the list costs O(n) time. You could just traverse the list backwards and save an extra iteration through the list.
Check out this solution:

def witnesses(heights):
    max_height = float('-inf')
    total = 0
    for i in range(len(heights) - 1, -1, -1):
        if heights[i] > max_height:
            total += 1
        max_height = max(heights[i], max_height)
    return total


print(witnesses([3, 6, 3, 4, 1]))
# 3
print(witnesses([3, 4, 4, 4, 1]))
# 2
print(witnesses([-1, -3, -7, -2]))
# 2

Thank you for your advice!!
You really point out the defects of my code.
I accepted your change and updated my code.

Awesome! Glad I could help!

you should have common sense that height can never be negative

humm, right for height but still a valid test case if the story change a bit