#include using namespace std; using LL = long long int; #define incID(i, l, r) for(int i = (l) ; i < (r); ++i) #define incII(i, l, r) for(int i = (l) ; i <= (r); ++i) #define decID(i, l, r) for(int i = (r) - 1; i >= (l); --i) #define decII(i, l, r) for(int i = (r) ; i >= (l); --i) #define inc(i, n) incID(i, 0, n) #define inc1(i, n) incII(i, 1, n) #define dec(i, n) decID(i, 0, n) #define dec1(i, n) decII(i, 1, n) #define inID(v, l, r) ((l) <= (v) && (v) < (r)) #define inII(v, l, r) ((l) <= (v) && (v) <= (r)) #define PB push_back #define EB emplace_back #define MP make_pair #define FI first #define SE second #define ALL(v) v.begin(), v.end() #define RALL(v) v.rbegin(), v.rend() auto setmin = [](auto & a, auto b) { return (b < a ? a = b, true : false); }; auto setmax = [](auto & a, auto b) { return (b > a ? a = b, true : false); }; auto setmineq = [](auto & a, auto b) { return (b <= a ? a = b, true : false); }; auto setmaxeq = [](auto & a, auto b) { return (b >= a ? a = b, true : false); }; auto fl = [](auto a, auto b) { assert(b != 0); return a / b - (a % b != 0 && ((a >= 0) != (b >= 0)) ? 1 : 0); }; auto ce = [](auto a, auto b) { assert(b != 0); return a / b + (a % b != 0 && ((a >= 0) == (b >= 0)) ? 1 : 0); }; auto mo = [](auto a, auto b) { assert(b != 0); a %= b; if(a < 0) { a += abs(b); } return a; }; LL gcd(LL a, LL b) { return (b == 0 ? a : gcd(b, a % b)); } LL lcm(LL a, LL b) { return a / gcd(a, b) * b; } #define bit(b, i) (((b) >> (i)) & 1) #define SI(v) static_cast(v.size()) #define RF(e, v) for(auto & e: v) #define until(e) while(! (e)) #define if_not(e) if(! (e)) #define ef else if #define UR assert(false) // ---- ---- template T MV(T v) { return v; } template auto MV(T v, int s, R... r) { return vector(s, MV(v, r...)); } #define LB(v, x) (lower_bound(ALL(v), x) - v.begin()) #define UB(v, x) (upper_bound(ALL(v), x) - v.begin()) int main() { LL n, x; cin >> n >> x; vector a(n), s(n + 1); inc(i, n) { cin >> a[i]; } inc(i, n) { s[i + 1] = s[i] + a[i]; } auto dp = MV(0, 2, n + 1, n + 1); vector> p; incII(d, 0, n) { incII(i, 0, n) { int j = i + d; if_not(j <= n) { continue; } if(d == 0) { dp[0][i][j] = dp[1][i][j] = +1; } if(d == 1) { dp[0][i][j] = dp[1][i][j] = -1; } if(d >= 1) { p.EB(i, j); } } } auto pr = [&]() { inc(i, n + 1) { inc(k, 2) { inc(j, n + 1) { printf("%2d ", dp[k][i][j]); } cout << " "; } cout << endl; } cout << endl; }; // pr(); RF(e, p) { int i = e.FI; int j = e.SE; dp[0][i][j] += dp[0][i + 1][j]; dp[1][i][j] += dp[1][i][j - 1]; if(dp[0][i][j] == 0 && j < n) { int r = UB(s, s[j] + x) - 1; assert(j + 1 <= r); if(j + 1 <= n) { dp[1][i][j + 1]++; } if(r <= n) { dp[1][i][r ]--; } } if(dp[1][i][j] == 0 && 0 < i) { int l = LB(s, s[i] - x); assert(l - 1 <= i - 1); if(0 <= i - 1) { dp[0][i - 1][j]++; } if(0 <= l - 1) { dp[0][l - 1][j]--; } } // pr(); } cout << (dp[0][0][n] != 0 ? "A" : "B") << endl; return 0; }