Solve in typescript please

You are given a string S consisting of N letters $\text{'}$a$\text{'}$ and$/$or $\text{'}$b$\text{'}.$ In one move, you can swap one letter for the other $(\text{'}$a$\text{'}$ for $\text{'}$b$\text{'}$ or $\text{'}$b$\text{'}$ for $\text{'}$a$\text{'}).$

Write a function so lution that, given such a string S $,$ returns the minimum number of moves required to obtain a string containing no instances of three identical consecutive letters.

Examples:

Given $S=$ "baaaaa", the function should return $1.$ The string without three identical consecutive letters which can be obtained in one move is "baabaa".

Solve in typescript please

Given S $=$ "baaabbaabbba", the function should return $2.$ There are four valid strings obtainable in two moves: for example, "bbaabbaabbaa".

Given $S=$ "baabab", the function should return $0.$

Write an efficient algorithm for the following assumptions:

N is an integer within the range $0.\mathrm{.}200,000$;

string $S$ is made only of the characters $\text{'}$a$\text{'}$ and$/$or $\text{'}$b$\text{'}.$