feat(sim): simulate n times instead of n days

1.in

+180 0.01
+

main.cpp

@@ -2,7 +2,7 @@
 #include "markov_chain.h"
 using namespace std;
 
-const int SIM_DAYS = 10000000;
+const int SIM_DAYS = 100000;
 
 int main ()
 {

markov_chain.cpp

@@ -15,7 +15,7 @@ using namespace std;
 
 
 State::State ()
-	: coupon_count ( EXPIRE_DAYS )
+	: coupon_count ( EXPIRE_DAYS, 0 )
 {
 
 }
@@ -30,44 +30,51 @@ int & State::operator [] ( int i )
 	return coupon_count[i];
 }
 
-pair<State, int> State::use_coupon ( int c ) const
+void State::pass_day ( int d )
+{
+	for ( int i = d; i < EXPIRE_DAYS; ++i ) {
+		coupon_count[i - d] = coupon_count[i];
+	}
+	for ( int i = max ( EXPIRE_DAYS - d, 0 ); i < EXPIRE_DAYS; ++i ) {
+		coupon_count[i] = 0;
+	}
+}
+
+int State::use_coupon ( int c )
 {
-	State result = *this;
 	int use_count = 0, current_use_count;
 	for ( int i = 0; i < EXPIRE_DAYS; ++i ) {
-		current_use_count = min ( result[i], c / COUPON_COST );
+		current_use_count = min ( coupon_count[i], c / COUPON_COST );
 		c -= COUPON_COST * current_use_count;
-		result[i] -= current_use_count;
+		coupon_count[i] -= current_use_count;
 		use_count += current_use_count;
 	}
-	return make_pair ( result, use_count );
+	return use_count;
 }
 
-State State::pass_day ( int c ) const
+void State::add_coupon ( int c )
 {
-	State result;
-	for ( int i = 1; i < EXPIRE_DAYS; ++i ) {
-		result[i - 1] = coupon_count[i];
-	}
-	result[EXPIRE_DAYS - 1] = c;
-	return result;
+	coupon_count[EXPIRE_DAYS - 1] = c;
 }
 
 
 
-double simulate_prob ( double lambda, double prob_day, int sim_days )
+double simulate_prob ( double lambda, double prob_day, int sim_times )
 {
 	mt19937 rand_gen ( static_cast < unsigned > ( chrono::system_clock::now ().time_since_epoch ().count () ) );
 	poisson_distribution < int > poisson ( lambda );
 	uniform_real_distribution < double > uniform ( 0.0, 1.0 );
 	State current_state;
 	long long total_cost = 0, used_coupon = 0;
-	for ( int day = 0; day < sim_days; ++day ) {
-		int current_cost = ( uniform ( rand_gen ) < prob_day ) ? poisson ( rand_gen ) : 0;
+	for ( int go_time = 0; go_time < sim_times; ++go_time ) {
+		int day = 1;
+		while ( uniform ( rand_gen ) >= prob_day ) ++day;
+		current_state.pass_day ( day );
+		int current_cost = poisson ( rand_gen );
 		total_cost += current_cost;
-		auto return_val = current_state.use_coupon ( current_cost );
-		used_coupon += return_val.second;
-		current_state = return_val.first.pass_day ( ( current_cost - return_val.second * COUPON_VALUE ) / COUPON_COST );
+		int current_coupon = current_state.use_coupon ( current_cost );
+		used_coupon += current_coupon;
+		current_state.add_coupon ( ( current_cost - current_coupon * COUPON_VALUE ) / COUPON_COST );
 	}
 	return ( static_cast < double > ( used_coupon * COUPON_VALUE ) / total_cost );
 }

markov_chain.h

@@ -16,12 +16,14 @@ public:
 	int operator [] ( int i ) const;
 	int & operator [] ( int i );
 
-	std::pair < State, int > use_coupon ( int c ) const;
+	void pass_day ( int d );
 
-	State pass_day ( int c ) const;
+	int use_coupon ( int c );
+
+	void add_coupon ( int c );
 
 private:
 	std::vector < int > coupon_count;   // i-th term indicates the number of coupons expired in the i-th day
 };
 
-double simulate_prob ( double lambda, double prob_day, int sim_days );
+double simulate_prob ( double lambda, double prob_day, int sim_times );