Ugu

1000ms

262144K

Description:

A binary string is a string consisting only of the characters 0 and 1. You are given a binary string $$$s_1 s_2 \ldots s_n$$$. It is necessary to make this string non-decreasing in the least number of operations. In other words, each character should be not less than the previous. In one operation, you can do the following:

Select an arbitrary index $$$1 \leq i \leq n$$$ in the string;
For all $$$j \geq i$$$, change the value in the $$$j$$$-th position to the opposite, that is, if $$$s_j = 1$$$, then make $$$s_j = 0$$$, and vice versa.

What is the minimum number of operations needed to make the string non-decreasing?

Input:

Each test consists of multiple test cases. The first line contains an integer $$$t$$$ ($$$1 \leq t \leq 10^4$$$) — the number of test cases. The description of test cases follows.

The first line of each test cases a single integer $$$n$$$ ($$$1 \leq n \leq 10^5$$$) — the length of the string.

The second line of each test case contains a binary string $$$s$$$ of length $$$n$$$.

It is guaranteed that the sum of $$$n$$$ over all test cases does not exceed $$$2 \cdot 10^5$$$.

Output:

For each test case, output a single integer — the minimum number of operations that are needed to make the string non-decreasing.

Sample Input:

Sample Output:

Note:

In the first test case, the string is already non-decreasing.

In the second test case, you can select $$$i = 1$$$ and then $$$s = \mathtt{01}$$$.

In the third test case, you can select $$$i = 1$$$ and get $$$s = \mathtt{010}$$$, and then select $$$i = 2$$$. As a result, we get $$$s = \mathtt{001}$$$, that is, a non-decreasing string.

In the sixth test case, you can select $$$i = 5$$$ at the first iteration and get $$$s = \mathtt{100001}$$$. Then choose $$$i = 2$$$, then $$$s = \mathtt{111110}$$$. Then we select $$$i = 1$$$, getting the non-decreasing string $$$s = \mathtt{000001}$$$.

Informação

Provedor Codeforces

Código CF1732B