Added a program file in the Java folder of Leetcode - MultiplyStrings.java

Leetcode/Java/MultiplyStrings.java

@@ -0,0 +1,40 @@
+/*Problem Number on leetcode: 43
+
+Problem name: Multiply Strings (Medium)
+
+Problem statement: Given two non-negative integers num1 and num2 represented as strings, return the product of num1 and num2, also represented as a string.
+Note: You must not use any built-in BigInteger library or convert the inputs to integer directly. 
+
+Example 1:
+Input: num1 = "2", num2 = "3"
+Output: "6"
+
+Example 2:
+Input: num1 = "123", num2 = "456"
+Output: "56088"
+
+*/
+
+//Sulution
+class Solution 
+{
+    public String multiply(String num1, String num2) 
+    {
+        if (num1.equals("0") || num2.equals("0")) 
+        {
+            return "0";
+        }
+        int m = num1.length() - 1, n = num2.length() - 1, carry = 0;
+        String product = "";
+        for (int i = 0; i <= m + n || carry != 0; ++i) 
+        {
+            for (int j = Math.max(0, i - n); j <= Math.min(i, m); ++j) 
+            {
+                carry += (num1.charAt(m - j) - '0') * (num2.charAt(n - i + j) - '0');
+            }
+            product += (char)(carry % 10 + '0');
+            carry /= 10;
+        }
+        return new StringBuilder(product).reverse().toString();
+    }
+}