Create combination.hpp

math/combination.hpp

@@ -0,0 +1,38 @@
+#pragma once
+
+#include<vector>
+#include<assert.h>
+
+namespace po167{
+struct combination{
+	int upper;
+	int MOD;
+	std::vector<long long> fact;
+	std::vector<long long> rev;
+	std::vector<long long> fact_rev;
+	combination(int max,long long mod):upper(max),MOD(mod),fact(max+1),rev(max+1),fact_rev(max+1){
+		for(long long i=0;i<=max;i++){
+			if(i<2){
+				fact[i]=1;
+				fact_rev[i]=1;
+				rev[i]=1;
+				continue;
+			}
+			fact[i]=(fact[i-1]*i)%mod;
+			rev[i]=mod-((mod/i)*rev[mod%i])%mod;
+			fact_rev[i]=(fact_rev[i-1]*rev[i])%mod;
+		}
+	}
+	long long Comb(int x,int y){
+		assert(upper>=x);
+		if (x<y||y<0||x<0) return 0;
+		return (((fact_rev[y]*fact_rev[x-y])%MOD)*fact[x])%MOD;
+	}
+	long long P(int x,int y){
+		assert(upper>=x);
+		if (x<y||y<0||x<0) return 0;
+		return (fact_rev[x-y]*fact[x])%MOD;
+	}
+};
+}
+using po167::combination;