B"You are given two binary strings a and b . A binary string is a string consisting of the characters '0' and '1'. Your task is to determine the maximum possible number k such that a prefix of string a of length k is a subsequence of string b . A sequence a is a subsequence of a sequence b if a can be obtained from b by the deletion of several (possibly, zero or all) elements. The first line consists of a single integer t ( 1 <= t <= 10^4 ) -- the number of test cases. The first line of each test case contains two integers n and m ( 1 <= n,m <= 2 cdot 10^5 ) -- the length of string a and the length of string b , respectively. The second line of each test case contains a binary string a of length n . The third line of each test case contains a binary string b of length m . It is guaranteed that the sum of values n over all test cases does not exceed 2 cdot 10^5 . Similarly, the sum of values m over all test cases does not exceed 2 cdot 10^5 . For each test case, output a single number -- the maximum k , such that the first k characters of a form a subsequence of b . In the first example, the string ' 10 ' is a subsequence of ' 1 color{red}11 color{red}0 ' but the string ' 100 ' is not. So the answer is 2 . In the fifth example, a =' 100 ', b =' 1 color{red}{10}1 color{red}0 ', whole string a is a subsequence of string b . So the answer is 3 . In the sixth example, string b does not contain ' 1 ' so the answer is 0 . "...