Create 1071-greatest-common-divisor-of-strings.java

java/1071-greatest-common-divisor-of-strings.java

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+class Solution {
+
+    // Helper function to calculate gcd using Euclidean algorithm
+    public int gcd(int a, int b){
+        if(b == 0){
+            return a;
+        }
+        return gcd(b, a%b);
+    }
+
+    /* 
+    Approach: If the string have a GCD, then str1 will be of the form m*GCD and str2 will be of the form n*GCD.
+    So, str1 + str2 = m*GCD + n*GCD = (m+n)*GCD, hence str1 + str2 should be equal to str2 + str1.
+    If the above condition is satisfied, then we can find the GCD of the lengths of the strings and return the substring of str1 of length GCD.
+    Else, return empty string.
+    */ 
+
+    public String gcdOfStrings(String str1, String str2) {
+        if((str1 + str2).equals(str2 + str1)){
+            int len1 = str1.length();
+            int len2 = str2.length();
+            int gcd = gcd(len1, len2);
+            return str1.substring(0, gcd);
+        }
+        return  "";
+    }
+}