Merge pull request FreeTymeKiyan#106 from FreeTymeKiyan/Kuang-043

Add Solution for Problem 043

C++/043_Multiply_Strings.cpp

@@ -0,0 +1,71 @@
+// 043. Multiply Strings
+/**
+ * Given two numbers represented as strings, return multiplication of the numbers as a string.
+ *
+ * Note: The numbers can be arbitrarily large and are non-negative
+ *
+ * Tags: Math, String
+ *
+ * Similar Problems: (M) Add Two Numbers, (E) Plus One, (E) Add Binary
+ *
+ * Author: Kuang Qin
+ */
+
+#include "stdafx.h"
+#include <string>
+#include <iostream>
+
+using namespace std;
+
+class Solution {
+public:
+    string multiply(string num1, string num2) {
+        if ((num1 == "0") || (num2 == "0"))
+        {
+            return "0";
+        }
+
+        // use an integer array to store multiplication products
+        int len1 = num1.size(), len2 = num2.size(), len = len1 + len2;
+        int *product = new int[len]();
+        for (int i = len1 - 1; i >= 0; i--)
+        {
+            for (int j = len2 - 1; j >= 0; j--)
+            {
+                product[i + j + 1] += (num1[i] - '0') * (num2[j] - '0');
+            }
+        }
+
+        // gather carry info to make each digit valid
+        for (int i = len - 1; i > 0; i--)
+        {
+            product[i - 1] += product[i] / 10;    // add carry to previous digit
+            product[i] = product[i] % 10;         // set current digit
+        }
+
+        // convert int into string
+        string res("");
+        if (product[0] != 0)    // first position could be zero
+        {
+            res += product[0] + '0';
+        }
+
+        for (int i = 1; i < len; i++)
+        {
+            res += product[i] + '0';
+        }
+
+        return res;
+    }
+};
+
+int _tmain(int argc, _TCHAR* argv[])
+{
+    string num1("8354"), num2("7890");
+    Solution mySolution;
+    string res = mySolution.multiply(num1, num2);
+    cout << num1 << " x " << num2 << " = " << res << endl;
+    system("pause");
+    return 0;
+}
+