Minimum Changes To Make Alternating Binary String
The idea behind this problem is to count the number of characters that need to be flipped in order to make the string alternating. We have two scenarios for an alternating string: it either starts with ‘0’ or it starts with ‘1’. We count the number of flips required for each case and then return the minimum of the two counts.
Python solution:


In this code:
We first create two expected strings
s1
ands2
of the same length ass
.s1
starts with ‘0’ ands2
starts with ‘1’.We then initialize two counters
count1
andcount2
to count the number of characters that need to be flipped to matchs1
ands2
, respectively.We iterate over the characters in
s
and compare them with the corresponding characters ins1
ands2
. If a character does not match, we increment the corresponding counter.Finally, we return the minimum of
count1
andcount2
which gives us the minimum number of operations needed to makes
alternating.
The greedy approach is about choosing the best option at each step with the hope that these local optimums will lead to a global optimum. In our context, the greedy choice is about minimizing the flips at each character position. We don’t look ahead to see how a choice will affect the future; we simply make the choice that seems best at the current step.
The Counter is used to count the discrepancies for two possible patterns. We’re making a greedy choice to minimize the number of flips for each pattern at each position.
The highlevel concepts used in this problem are:
 Python’s Counter to count the number of discrepancies.
 The Greedy Algorithm to make the choice that minimizes the number of flips at each step.