Update Discrete Logarithm.cpp

Author: Ashishgup1

Discrete Logarithm.cpp

@@ -50,6 +50,68 @@ int discreteLog(int a, int b, int m)
 	}
 }
 
+------------------------------------------------------------------------------------------------------------------------------------
+//Faster Implementation
+	
+#include <bits/stdc++.h>
+#include <ext/pb_ds/assoc_container.hpp>
+using namespace __gnu_pbds;
+using namespace std;
+ 
+#define IOS ios::sync_with_stdio(0); cin.tie(0); cout.tie(0);
+#define endl "\n"
+#define int long long
+
+long long pow(long long a, long long b, long long m)
+{
+	long long ans=1;
+	while(b)
+	{
+		if(b&1)
+			ans=(ans*a)%m;
+		b/=2;
+		a=(a*a)%m;
+	}
+	return ans;
+}
+
+int discreteLog(int a, int b, int m)
+{
+	a %= m, b %= m;
+	if(b == 1)
+		return 0;
+	int cnt = 0;
+	long long t = 1;
+	for(int curg=__gcd(a, m);curg!=1;curg=__gcd(a, m))
+	{
+		if(b % curg)
+			return -1;
+		b /= curg, m /= curg, t = (t * a / curg) % m;
+		cnt++;
+		if(b == t)
+			return cnt;
+	}
+
+	gp_hash_table<int, int> hash;
+	int mid = ((int)sqrt(1.0 * m) + 1);
+	long long base = b;
+	for(int i=0;i<mid;i++)
+	{
+		hash[base] = i;
+		base = base * a % m;
+	}
+
+	base = pow(a, mid, m);
+	long long cur = t;
+	for(int i=1;i<=mid+1;i++)
+	{
+		cur = cur * base % m;
+		auto it = hash.find(cur);
+		if(it != hash.end())
+			return i * mid - it->second + cnt;
+	}
+}
+
 //Problem 1: https://codeforces.com/gym/101853/problem/G
 //Solution 1: https://codeforces.com/gym/101853/submission/50273547