feat(sim): use geometric distribution to get the next day

.gitignore

@@ -2,3 +2,6 @@ main
 Debug
 .vs
 *.vcxproj*
+*.in
+*.out
+tmp

main.cpp

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

markov_chain.cpp

@@ -63,12 +63,11 @@ 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 );
+	geometric_distribution < int > geometric ( prob_day );
 	State current_state;
 	long long total_cost = 0, used_coupon = 0;
 	for ( int go_time = 0; go_time < sim_times; ++go_time ) {
-		int day = 1;
-		while ( uniform ( rand_gen ) >= prob_day ) ++day;
+		int day = geometric ( rand_gen ) + 1;
 		current_state.pass_day ( day );
 		int current_cost = poisson ( rand_gen );
 		total_cost += current_cost;