Create add-strings.cpp

Author: kamyu104

C++/add-strings.cpp

@@ -0,0 +1,25 @@
+// Time:  O(n)
+// Space: O(1)
+
+class Solution {
+public:
+    string addStrings(string num1, string num2) {
+        string result;
+
+        for (int i = num1.size() - 1, j = num2.size() - 1, carry = 0;
+             i >= 0 || j >= 0 || carry;
+             carry /= 10) {
+
+            if (i >= 0) {
+                carry += num1[i--] - '0';
+            }
+            if (j >= 0) {
+                carry += num2[j--] - '0';
+            }
+            result += to_string(carry % 10);
+        }
+        reverse(result.begin(), result.end());
+
+        return result;
+    }
+};