algo(harshadNumbers): add algo + light docs + problem statement picture

Author: domfarolino

src/algorithm_practice/Number_Algorithms/harshadNumbers/README.md

@@ -0,0 +1,18 @@
+# Harshad Numbers
+
+Source:
+
+ - ACMICPC Regionals 2018 Hosted @ University of Cincinnati
+
+![harshad numbers problem statement picture](./harshadNumbers.jpg)
+
+This is a relatively straight-forward brute-force algorithm, which
+practically does not need explained at all.
+
+# Complexity analysis
+
+ - Time complexity: O(log(n)\*k), where n = the nth harshad number, and k is the
+   gap between the input number and the next harshad number (I don't know the exact
+   relationship between/formula of the harshad numbers so I am just generalizing the
+   complexity to this text)
+ - Space complexity: O(1)

src/algorithm_practice/Number_Algorithms/harshadNumbers/harsh.cpp

@@ -0,0 +1,25 @@
+#include <iostream>
+
+// Source: ACM ICPC 2018
+
+bool harshad(long in) {
+  long saveIn = in;
+  int sum = 0;
+  while (in) {
+    sum += in % 10;
+    in /= 10;
+  }
+
+  return (saveIn % sum == 0);
+}
+
+int main() {
+  long input;
+  std::cin >> input;
+
+  while (!harshad(input))
+    input++;
+
+  std::cout << input << std::endl;
+  return 0;
+}