CF1437B.Reverse Binary Strings

You are given a string $s$ of even length $n$ . String $s$ is binary, in other words, consists only of 0's and 1's.

String $s$ has exactly $\frac{n}{2}$ zeroes and $\frac{n}{2}$ ones ( $n$ is even).

In one operation you can reverse any substring of $s$ . A substring of a string is a contiguous subsequence of that string.

What is the minimum number of operations you need to make string $s$ alternating? A string is alternating if $s_i \neq s_{i + 1}$ for all $i$ . There are two types of alternating strings in general: 01010101... or 10101010...

The first line contains a single integer $t$ ( $1 \le t \le 1000$ ) — the number of test cases.

The first line of each test case contains a single integer $n$ ( $2 \le n \le 10^5$ ; $n$ is even) — the length of string $s$ .

The second line of each test case contains a binary string $s$ of length $n$ ( $s_i \in$ {0, 1}). String $s$ has exactly $\frac{n}{2}$ zeroes and $\frac{n}{2}$ ones.

It's guaranteed that the total sum of $n$ over test cases doesn't exceed $10^5$ .

For each test case, print the minimum number of operations to make $s$ alternating.

In the first test case, string 10 is already alternating.

In the second test case, we can, for example, reverse the last two elements of $s$ and get: 0110 $\rightarrow$ 0101.

In the third test case, we can, for example, make the following two operations:

1. 11101000 $\rightarrow$ 10101100;
2. 10101100 $\rightarrow$ 10101010.