ADDED   SRM/663-U/1A.cpp
Index: SRM/663-U/1A.cpp
==================================================================
--- SRM/663-U/1A.cpp
+++ SRM/663-U/1A.cpp
@@ -0,0 +1,99 @@
+#include <iostream>
+#include <sstream>
+#include <iomanip>
+#include <vector>
+#include <string>
+#include <map>
+#include <set>
+#include <algorithm>
+#include <numeric>
+#include <iterator>
+#include <functional>
+#include <complex>
+#include <queue>
+#include <stack>
+#include <cmath>
+#include <cassert>
+#include <tuple>
+using namespace std;
+typedef long long LL;
+typedef complex<double> CMP;
+
+class ABBADiv1 { public:
+	string canObtain(string initial, string target)
+	{
+		return can(target, initial) ? "Possible" : "Impossible";
+	}
+
+	map<string, bool> memo;
+	bool can(const string& X, const string& S)
+	{
+		if(X == S)
+			return true;
+		if(X.size() < S.size())
+			return false;
+		if(memo.count(X))
+			return memo[X];
+		if(X[X.size()-1] == 'A' && can(X.substr(0, X.size()-1), S)) return memo[X] = true;
+		if(X[0] == 'B' && can(rev(X.substr(1, X.size())), S)) return memo[X] = true;
+		return memo[X] = false;
+	}
+
+	string rev(const string& x) { return string(x.rbegin(), x.rend()); }
+};
+
+// BEGIN CUT HERE
+#include <ctime>
+double start_time; string timer()
+ { ostringstream os; os << " (" << int((clock()-start_time)/CLOCKS_PER_SEC*1000) << " msec)"; return os.str(); }
+template<typename T> ostream& operator<<(ostream& os, const vector<T>& v)
+ { os << "{ ";
+   for(typename vector<T>::const_iterator it=v.begin(); it!=v.end(); ++it)
+   os << '\"' << *it << '\"' << (it+1==v.end() ? "" : ", "); os << " }"; return os; }
+void verify_case(const string& Expected, const string& Received) {
+ bool ok = (Expected == Received);
+ if(ok) cerr << "PASSED" << timer() << endl;  else { cerr << "FAILED" << timer() << endl;
+ cerr << "\to: \"" << Expected << '\"' << endl << "\tx: \"" << Received << '\"' << endl; } }
+#define CASE(N) {cerr << "Test Case #" << N << "..." << flush; start_time=clock();
+#define END	 verify_case(_, ABBADiv1().canObtain(initial, target));}
+int main(){
+
+CASE(0)
+	string initial = "A"; 
+	string target = "BABA"; 
+	string _ = "Possible"; 
+END
+CASE(1)
+	string initial = "BAAAAABAA"; 
+	string target = "BAABAAAAAB"; 
+	string _ = "Possible"; 
+END
+CASE(2)
+	string initial = "A"; 
+	string target = "ABBA"; 
+	string _ = "Impossible"; 
+END
+CASE(3)
+	string initial = "AAABBAABB"; 
+	string target = "BAABAAABAABAABBBAAAAAABBAABBBBBBBABB"; 
+	string _ = "Possible"; 
+END
+CASE(4)
+	string initial = "AAABAAABB"; 
+	string target = "BAABAAABAABAABBBAAAAAABBAABBBBBBBABB"; 
+	string _ = "Impossible"; 
+END
+/*
+CASE(5)
+	string initial = ; 
+	string target = ; 
+	string _ = ; 
+END
+CASE(6)
+	string initial = ; 
+	string target = ; 
+	string _ = ; 
+END
+*/
+}
+// END CUT HERE

ADDED   SRM/663-U/1B-U.cpp
Index: SRM/663-U/1B-U.cpp
==================================================================
--- SRM/663-U/1B-U.cpp
+++ SRM/663-U/1B-U.cpp
@@ -0,0 +1,213 @@
+#include <iostream>
+#include <sstream>
+#include <iomanip>
+#include <vector>
+#include <string>
+#include <map>
+#include <set>
+#include <algorithm>
+#include <numeric>
+#include <iterator>
+#include <functional>
+#include <complex>
+#include <queue>
+#include <stack>
+#include <cmath>
+#include <cassert>
+#include <tuple>
+using namespace std;
+typedef long long LL;
+typedef complex<double> CMP;
+
+static const unsigned MODVAL = 1000000007;
+struct mint
+{
+	unsigned val;
+	mint():val(0){}
+	mint(int      x):val(x%MODVAL) {}
+	mint(unsigned x):val(x%MODVAL) {}
+	mint(LL       x):val(x%MODVAL) {}
+};
+mint& operator+=(mint& x, mint y) { return x = x.val+y.val; }
+mint& operator-=(mint& x, mint y) { return x = x.val-y.val+MODVAL; }
+mint& operator*=(mint& x, mint y) { return x = LL(x.val)*y.val; }
+mint operator+(mint x, mint y) { return x+=y; }
+mint operator-(mint x, mint y) { return x-=y; }
+mint operator*(mint x, mint y) { return x*=y; }
+
+mint POW(mint x, LL e) { mint v=1; for(;e;x*=x,e>>=1) if(e&1) v*=x; return v; }
+mint& operator/=(mint& x, mint y) { return x *= POW(y, MODVAL-2); }
+mint operator/(mint x, mint y) { return x/=y; }
+
+vector<mint> FAC_(1,1);
+mint FAC(LL n) { while( FAC_.size()<=n ) FAC_.push_back( FAC_.back()*LL(FAC_.size()) ); return FAC_[n]; }
+
+// nCk :: O(log MODVAL) time, O(n) space.
+mint C(LL n, LL k) { return k<0 || n<k ? 0 : FAC(n) / (FAC(k) * FAC(n-k)); }
+
+// nCk :: O(1) time, O(n^2) space.
+vector< vector<mint> > CP_;
+mint C(int n, int k) {
+	while( CP_.size() <= n ) {
+		int nn = CP_.size();
+		CP_.push_back(vector<mint>(nn+1,1));
+		for(int kk=1; kk<nn; ++kk)
+			CP_[nn][kk] = CP_[nn-1][kk-1] + CP_[nn-1][kk];
+	}
+	return k<0 || n<k ? 0 : CP_[n][k];
+}
+
+class ChangingChange { public:
+	vector <int> countWays(vector <int> ways, vector <int> valueRemoved, vector <int> numRemoved)
+	{
+		const int D = ways.size()-1;
+
+		vector<mint> coins(1, 0);
+		for(int v=1; v<=D; ++v)
+			coins.push_back(ways[v] - eval(coins,v));
+
+		vector<int> ans;
+		for(int q=0; q<valueRemoved.size(); ++q) {
+			const int v=valueRemoved[q], n=numRemoved[q];
+			coins[v] -= n; // or += MODVAL-n, meaning mult (1+x^v)^(MODVAL-n)
+			// then if cur is known and (1+x^v)^(MODVAL-n) is known,
+			// O(D) to calc eval(coins,D)
+			ans.push_back(eval(coins,D).val);
+			coins[v] += n;
+		}
+		return ans;
+	}
+
+	// Calc \Pi_v (1 + x^v)^c[v] 's coeefficient at x^D
+	//   c[v] may be very large
+	//   D <= 2000
+	//   v <= 2000
+	mint eval(const vector<mint>& c, int D)
+	{
+		vector<mint> cur(D+1, 0);
+		cur[0] = 1;
+		for(int v=1; v<c.size(); ++v) {
+			cur = polymul(cur, polypow(v, c[v].val, D), D);
+		}
+		return D<cur.size() ? cur[D] : 0;
+	}
+
+	vector<mint> polymul(const vector<mint>& a, const vector<mint>& b, int D)
+	{
+		int maxD = max<int>(D, (a.size()-1)*(b.size()-1));
+		vector<mint> c(maxD+1);
+		for(int i=0; i<a.size(); ++i)
+		for(int k=0; k<b.size(); ++k)
+			if(i+k<=maxD)
+				c[i+k] += a[i]*b[k];
+		return c;
+	}
+	vector<mint> polypow(int V, int K, int D)
+	{
+		vector<mint> poly;
+		// (1+x^V)^K upto x^D
+		mint Ckd = 1;
+		for(int d=0; d<=K; ++d) {
+			LL dd = LL(d)*V;
+			if(dd > D)
+				break;
+			poly.resize(int(dd)+1);
+			poly[int(dd)] = Ckd;
+
+			Ckd *= (K-d);
+			Ckd /= (d+1);
+		}
+		return poly;
+	}
+};
+
+// BEGIN CUT HERE
+#include <ctime>
+double start_time; string timer()
+ { ostringstream os; os << " (" << int((clock()-start_time)/CLOCKS_PER_SEC*1000) << " msec)"; return os.str(); }
+template<typename T> ostream& operator<<(ostream& os, const vector<T>& v)
+ { os << "{ ";
+   for(typename vector<T>::const_iterator it=v.begin(); it!=v.end(); ++it)
+   os << '\"' << *it << '\"' << (it+1==v.end() ? "" : ", "); os << " }"; return os; }
+void verify_case(const vector <int>& Expected, const vector <int>& Received) {
+ bool ok = (Expected == Received);
+ if(ok) cerr << "PASSED" << timer() << endl;  else { cerr << "FAILED" << timer() << endl;
+ cerr << "\to: " << Expected << endl << "\tx: " << Received << endl; } }
+#define CASE(N) {cerr << "Test Case #" << N << "..." << flush; start_time=clock();
+#define END	 verify_case(_, ChangingChange().countWays(ways, valueRemoved, numRemoved));}
+int main(){
+
+CASE(0)
+	int ways_[] = {1, 4, 6};
+	  vector <int> ways(ways_, ways_+sizeof(ways_)/sizeof(*ways_)); 
+	int valueRemoved_[] = {1, 1, 1};
+	  vector <int> valueRemoved(valueRemoved_, valueRemoved_+sizeof(valueRemoved_)/sizeof(*valueRemoved_)); 
+	int numRemoved_[] = {1, 2, 3};
+	  vector <int> numRemoved(numRemoved_, numRemoved_+sizeof(numRemoved_)/sizeof(*numRemoved_)); 
+	int __[] = {3, 1, 0 };
+	  vector <int> _(__, __+sizeof(__)/sizeof(*__)); 
+END
+CASE(1)
+	int ways_[] = {1, 2, 1, 0, 0, 0, 0, 0, 7};
+	  vector <int> ways(ways_, ways_+sizeof(ways_)/sizeof(*ways_)); 
+	int valueRemoved_[] = {8, 8, 1, 1};
+	  vector <int> valueRemoved(valueRemoved_, valueRemoved_+sizeof(valueRemoved_)/sizeof(*valueRemoved_)); 
+	int numRemoved_[] = {1, 7, 1, 2};
+	  vector <int> numRemoved(numRemoved_, numRemoved_+sizeof(numRemoved_)/sizeof(*numRemoved_)); 
+	int __[] = {6, 0, 7, 7 };
+	  vector <int> _(__, __+sizeof(__)/sizeof(*__)); 
+END
+CASE(2)
+	int ways_[] = {1, 2, 3, 6, 9, 14};
+	  vector <int> ways(ways_, ways_+sizeof(ways_)/sizeof(*ways_)); 
+	int valueRemoved_[] = {1, 2, 3, 4, 5, 1, 2, 3, 4, 5};
+	  vector <int> valueRemoved(valueRemoved_, valueRemoved_+sizeof(valueRemoved_)/sizeof(*valueRemoved_)); 
+	int numRemoved_[] = {1, 1, 1, 1, 1, 2, 2, 2, 2, 2};
+	  vector <int> numRemoved(numRemoved_, numRemoved_+sizeof(numRemoved_)/sizeof(*numRemoved_)); 
+	int __[] = {9, 10, 11, 12, 13, 6, 8, 8, 10, 12 };
+	  vector <int> _(__, __+sizeof(__)/sizeof(*__)); 
+END
+CASE(3)
+	int ways_[] = {1, 0};
+	  vector <int> ways(ways_, ways_+sizeof(ways_)/sizeof(*ways_)); 
+	int valueRemoved_[] = {1, 1};
+	  vector <int> valueRemoved(valueRemoved_, valueRemoved_+sizeof(valueRemoved_)/sizeof(*valueRemoved_)); 
+	int numRemoved_[] = {1, 1000000};
+	  vector <int> numRemoved(numRemoved_, numRemoved_+sizeof(numRemoved_)/sizeof(*numRemoved_)); 
+	int __[] = {1000000006, 999000007 };
+	  vector <int> _(__, __+sizeof(__)/sizeof(*__)); 
+END
+CASE(4)
+	int ways_[] = {1, 2, 3, 6, 9, 14};
+	  vector <int> ways(ways_, ways_+sizeof(ways_)/sizeof(*ways_)); 
+	int valueRemoved_[] = {1, 3, 5};
+	  vector <int> valueRemoved(valueRemoved_, valueRemoved_+sizeof(valueRemoved_)/sizeof(*valueRemoved_)); 
+	int numRemoved_[] = {1000000, 4, 2};
+	  vector <int> numRemoved(numRemoved_, numRemoved_+sizeof(numRemoved_)/sizeof(*numRemoved_)); 
+	int __[] = {34955525, 2, 12 };
+	  vector <int> _(__, __+sizeof(__)/sizeof(*__)); 
+END
+/*
+CASE(5)
+	int ways_[] = ;
+	  vector <int> ways(ways_, ways_+sizeof(ways_)/sizeof(*ways_)); 
+	int valueRemoved_[] = ;
+	  vector <int> valueRemoved(valueRemoved_, valueRemoved_+sizeof(valueRemoved_)/sizeof(*valueRemoved_)); 
+	int numRemoved_[] = ;
+	  vector <int> numRemoved(numRemoved_, numRemoved_+sizeof(numRemoved_)/sizeof(*numRemoved_)); 
+	int __[] = ;
+	  vector <int> _(__, __+sizeof(__)/sizeof(*__)); 
+END
+CASE(6)
+	int ways_[] = ;
+	  vector <int> ways(ways_, ways_+sizeof(ways_)/sizeof(*ways_)); 
+	int valueRemoved_[] = ;
+	  vector <int> valueRemoved(valueRemoved_, valueRemoved_+sizeof(valueRemoved_)/sizeof(*valueRemoved_)); 
+	int numRemoved_[] = ;
+	  vector <int> numRemoved(numRemoved_, numRemoved_+sizeof(numRemoved_)/sizeof(*numRemoved_)); 
+	int __[] = ;
+	  vector <int> _(__, __+sizeof(__)/sizeof(*__)); 
+END
+*/
+}
+// END CUT HERE

Index: lib/numeric/modArith.cpp
==================================================================
--- lib/numeric/modArith.cpp
+++ lib/numeric/modArith.cpp
@@ -27,11 +27,11 @@
 mint POW(mint x, LL e) { mint v=1; for(;e;x*=x,e>>=1) if(e&1) v*=x; return v; }
 mint& operator/=(mint& x, mint y) { return x *= POW(y, MODVAL-2); }
 mint operator/(mint x, mint y) { return x/=y; }
 
 vector<mint> FAC_(1,1);
-mint FAC(LL n) { while( FAC_.size()<=n ) FAC_.push_back( FAC_.back()*FAC_.size() ); return FAC_[n]; }
+mint FAC(LL n) { while( FAC_.size()<=n ) FAC_.push_back( FAC_.back()*LL(FAC_.size()) ); return FAC_[n]; }
 
 // nCk :: O(log MODVAL) time, O(n) space.
 mint C(LL n, LL k) { return k<0 || n<k ? 0 : FAC(n) / (FAC(k) * FAC(n-k)); }
 
 // nCk :: O(1) time, O(n^2) space.