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  Hackerank quetion... We have see  that lists are mutable (they can be changed), and tuples are immutable (they cannot be changed). Let's try to understand this with an example. You are given an immutable string, and you want to make changes to its. Example... >>> string = "abracadabra" You can access an index by: >>> print string[5] a What if you would like to assign a value? >>> string[5] = 'k' Traceback (most recent call last): File "<stdin>", line 1, in <module> TypeError: 'str' object does not support item assignment How would you approach this? One solution is to convert the string to a list and then change the value. Example >>> string = "abracadabra" >>> l = list(string) >>> l[5] = 'k' >>> string = ''.join(l) >>> print string abrackdabra Another approach is to slice the string and join it back. Example >>> string = st...

 THE  An avid hiker keeps meticulous records of their hikes. During the last hike that took exactly     steps, for every step it was noted if it was an   uphill ,   , or a   downhill ,     step. Hikes always start and end at sea level, and each step up or down represents a     unit change in altitude. We define the following terms: A  mountain  is a sequence of consecutive steps  above  sea level, starting with a step  up  from sea level and ending with a step  down  to sea level. A  valley  is a sequence of consecutive steps  below  sea level, starting with a step  down  from sea level and ending with a step  up  to sea level. Given the sequence of  up  and  down  steps during a hike, find and print the number of  valleys  walked through. Example   The hiker first enters a valley   units deep. Then they climb...