###################################################################### # Given a

Question

######################################################################

# Given a sequence, S, an integer i < len(S) and a second integer j,

# return a (new) sequence consisting of S with the last i characters

# repeated exactly j times.

#

# Note: i > 0 should also be required, else -0 will repeat the whole

# sequence, not the 0th last element.

#

# >>> extendSequence([1, 2, 3], 2, 2)

# [1, 2, 3, 2, 3]

# >>> extendSequence((1, 3, 5, 6), 2, 3)

# (1, 3, 5, 6, 5, 6, 5, 6)

#

def extendSequence(S, i, j):

return(S[:-i] + j*S[-i:])

For the solution, i don't understand why there is a [:-i]

Can you please explain how they found this out

Explanation / Answer

S[:-i] lives out last i items from list S S[-i:] gives last i items from list S j * S[-i:] gives last i items from list S, repeated j times. S[:-i] + j*S[i:] -> gives a list of first len(S)-i elements concatenated with last i items repeated j times.

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