Merge pull request #746 from pradhuman131/master

added gcd of big numbers

Author: matthewsamuel95

Math/gcd/gcd_big_number.cpp

@@ -0,0 +1,56 @@
+#include<bits/stdc++.h> 
+using namespace std; 
+typedef long long int ll; 
+  
+// function to find gcd of two integer numbers 
+ll gcd(ll a, ll b) 
+{ 
+    if (!a) 
+       return b; 
+    return gcd(b%a,a); 
+} 
+  
+// Here 'a' is integer and 'b' is string. 
+// The idea is to make the second number (represented 
+// as b) less than and equal to first number by 
+// calculating its mod with first integer number 
+// using basic mathematics 
+ll reduceB(ll a, char b[]) 
+{ 
+    // Initialize result 
+    ll mod = 0; 
+  
+    // calculating mod of b with a to make 
+    // b like 0 <= b < a 
+    for (int i=0; i<strlen(b); i++) 
+        mod = (mod*10 + b[i] - '0')%a; 
+  
+    return mod; // return modulo 
+} 
+  
+// This function returns GCD of 'a' and 'b' 
+// where b can be very large and is represented 
+// as a character array or string 
+ll gcdLarge(ll a, char b[]) 
+{ 
+    // Reduce 'b' (second number) after modulo with a 
+    ll num = reduceB(a, b); 
+  
+    // gcd of two numbers 
+    return gcd(a, num); 
+} 
+  
+// Driver program 
+int main() 
+{ 
+    // first number which is integer 
+    ll a = 1221; 
+  
+    // second number is represented as string because 
+    // it can not be handled by integer data type 
+    char b[] = "1234567891011121314151617181920212223242526272829"; 
+  
+    cout << gcdLarge(a, b); 
+  
+    return 0; 
+}