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//╚══██╔══╝██║████╗░██║  ██║░░░░░██╔════╝
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//░░░██║░░░██║██║░╚███║  ███████╗███████╗
//░░░╚═╝░░░╚═╝╚═╝░░╚══╝  ╚══════╝╚══════╝
//   __________________
//  | ________________ |
//  ||          ____  ||
//  ||   /\    |      ||
//  ||  /__\   |      ||
//  || /    \  |____  ||
//  ||________________||
//  |__________________|
//  \###################\
//   \###################\
//    \        ____       \
//     \_______\___\_______\
// An AC a day keeps the doctor away.

#include <bits/stdc++.h>
#include <ext/pb_ds/assoc_container.hpp>
using namespace __gnu_pbds;
using namespace std;
template<class T> using ordered_set = tree<T, null_type, less<T>, rb_tree_tag, tree_order_statistics_node_update>;
#define vt vector
#define all(x) begin(x), end(x)
#define allr(x) rbegin(x), rend(x)
#define ub upper_bound
#define lb lower_bound
#define db double
#define ld long db
#define ll int64_t
#define vll vt<ll>  
#define vvll vt<vll>
#define pll pair<ll, ll>    
#define vpll vt<pll>
#define vc vt<char> 
#define vvc vt<vc>
#define vi vt<int>
#define vvi vt<vi>
#define vvvi vt<vvi>
#define pii pair<int, int>
#define vpii vt<pii>
#define vs vt<string>
#define vvs vt<vs>
#define vb vt<bool>
#define vvb vt<vb>
#define vvpii vt<vpii>
#define vd vt<db>
#define ar(x) array<int, x>
#define var(x) vt<ar(x)>
#define vvar(x) vt<var(x)>
#define pq priority_queue
#define mset(m, v) memset(m, v, sizeof(m))
#define pb push_back
#define ff first
#define ss second
#define sv string_view
#define MP make_pair
#define MT make_tuple
#define rsz resize
#define sum(x) accumulate(all(x), 0LL)
#define srt(x) sort(all(x))
#define srtR(x) sort(allr(x))
#define srtU(x) sort(all(x)), (x).erase(unique(all(x)), (x).end())
#define SORTED(x) is_sorted(all(x))
#define rev(x) reverse(all(x))
#define gcd(a, b) __gcd(a, b)
#define lcm(a, b) (a * b) / gcd(a, b)
#define MAX(a) *max_element(all(a)) 
#define MIN(a) *min_element(all(a))

//SGT DEFINE
#define lc i * 2 + 1
#define rc i * 2 + 2
#define lp lc, left, middle
#define rp rc, middle + 1, right
#define entireTree 0, 0, n - 1
#define midPoint left + (right - left) / 2
#define pushDown push(i, left, right)
#define iterator int i, int left, int right

#define IOS ios_base::sync_with_stdio(false); cin.tie(0); cout.tie(0)

struct custom {
    static const uint64_t C = 0x9e3779b97f4a7c15; const uint32_t RANDOM = std::chrono::steady_clock::now().time_since_epoch().count();
    size_t operator()(uint64_t x) const { return __builtin_bswap64((x ^ RANDOM) * C); }
    size_t operator()(const std::string& s) const { size_t hash = std::hash<std::string>{}(s); return hash ^ RANDOM; } };
template <class K, class V> using umap = std::unordered_map<K, V, custom>; template <class K> using uset = std::unordered_set<K, custom>;
    
template<typename T1, typename T2>
std::ostream& operator<<(std::ostream& o, const std::pair<T1, T2>& p) { return o << "{" << p.ff << " , " << p.ss << "}"; }
auto operator<<(auto &o, const auto &x) -> decltype(end(x), o) {
    o << "{"; int i = 0; for (const auto &e : x) { if (i++) o << " , "; o << e; } return o << "}";
}
    
template <typename T1, typename T2>  istream &operator>>(istream& in, pair<T1, T2>& input) {    return in >> input.ff >> input.ss; }
    
template <typename T> istream &operator>>(istream &in, vector<T> &v) { for (auto &el : v) in >> el; return in; }
    
template<typename K, typename V>
auto operator<<(std::ostream &o, const std::map<K, V> &m) -> std::ostream& {
    o << "{"; int i = 0;
    for (const auto &[key, value] : m) { if (i++) o << " , "; o << key << " : " << value; }
    return o << "}";
}
    
template<typename T> vt<T> uniqued(vt<T> arr) {  srtU(arr); return arr; }

#ifdef LOCAL
#define debug(x...) debug_out(#x, x)
void debug_out(const char* names) { std::cerr << std::endl; }
template <typename T, typename... Args>
void debug_out(const char* names, T value, Args... args) {
    const char* comma = strchr(names, ',');
    std::cerr << "[" << (comma ? std::string(names, comma) : names) << " = " << value << "]";
    if (sizeof...(args)) { std::cerr << ", "; debug_out(comma + 1, args...); }   
    else { std::cerr << std::endl; }
}
#define startClock clock_t tStart = clock();
#define endClock std::cout << std::fixed << std::setprecision(10) << "\nTime Taken: " << (double)(clock() - tStart) / CLOCKS_PER_SEC << " seconds" << std::endl;
#else
#define debug(...)
#define startClock
#define endClock

#endif
mt19937 rng(chrono::steady_clock::now().time_since_epoch().count());

#define eps 1e-9
#define M_PI 3.14159265358979323846
const static ll INF = 1LL << 62;
const static int inf = 1e9 + 33;
const static int MK = 20;
const static int MX = 2e6 + 5;
const static int MOD = 1e9 + 7;
int pct(ll x) { return __builtin_popcountll(x); }
const vvi dirs = {{-1, 0}, {1, 0}, {0, -1}, {0, 1}, {1, 1}, {-1, -1}, {1, -1}, {-1, 1}}; // UP, DOWN, LEFT, RIGHT
const vc dirChar = {'U', 'D', 'L', 'R'};
int modExpo(ll base, ll exp, ll mod) { ll res = 1; base %= mod; while(exp) { if(exp & 1) res = (res * base) % mod; base = (base * base) % mod; exp >>= 1; } return res; }
vi primes, first_divisor(MX);  
bitset<MX> primeBits;
void generatePrime() {  primeBits.set(2);   
    for(int i = 3; i < MX; i += 2) primeBits.set(i);
    for(int i = 2; i * i < MX; i += (i == 2 ? 1 : 2)) {    
        if(primeBits[i]) {  
            for(int j = i; j * i < MX; j += 2) {    primeBits.reset(i * j); }
        }
    }
    for(int i = 2; i < MX; i++) {    
        if(primeBits[i]) {  
            for(int j = i; j < MX; j += i) {    if(first_divisor[j] == 0) first_divisor[j] = i; }
        }
    }
    for(int i = 0; i < MX; i++ ) {  if(primeBits[i]) {  primes.pb(i); } }   
}

template<class T>   
class SGT { 
    public: 
    int n;  
    vt<T> root;
    SGT(int n) {    
        this->n = n;
        root.rsz(n * 4, {0, 0, 0});    
    }
    
    void update(int id, int val, int x) {  
        update(entireTree, id, val, x);
    }
    
    void update(iterator, int id, int val, int x) {  
        if(left == right) { 
            root[i][val] += x;
            return;
        }
        int middle = midPoint;  
        if(id <= middle) update(lp, id, val, x);   
        else update(rp, id, val, x);   
        root[i] = merge(root[lc], root[rc]);
    }

    T merge(T left, T right) { // 0 : zero's element, 1 : one's element, 2 : ans of subsequence 
        T res;  
        res[2] = left[2] + right[2] + left[0] * right[1];
        res[0] = left[0] + right[0];    
        res[1] = left[1] + right[1];
        return res;
    }
	
	ll get() {
		return root[0][2];
	}

};

void solve() {
    int n, k; cin >> n >> k;
    string s; cin >> s; 
    vi a;   
    SGT<array<ll, 3>> root(n);
    for(int i = 0; i < n; i++) {    
        if(s[i] == 'A') {   
            root.update(i, 0, 1);
        }
        else if(s[i] == 'B') {  
            root.update(i, 1, 1);
        }
        else if((int)a.size() < k && s[i] == '?') {  
            a.pb(i);
        }
    }
    for(auto& x : a) {  
        root.update(x, 0, 1);
    }
    ll res = root.get();
    int j = n - 1;  
    rev(a); 
    for(auto& x : a) {  
        root.update(x, 0, -1);
        while(s[j] != '?') {    
            j--;
        }
        root.update(j, 1, 1);
        j--;
        res = max(res, root.get());
    }
    cout << res << endl;
}

signed main() {
    IOS;
    startClock
    //generatePrime();

    int t = 1;
    cin >> t;
    for(int i = 1; i <= t; i++) {   
        //cout << "Case #" << i << ": ";  
        solve();
    }

    //endClock
    return 0;
}

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