add kata

5kyu/count-ip-addresses/description.md

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+Implement a function that receives two IPv4 addresses, and returns the number of addresses between them (including the first one, excluding the last one).
+
+All inputs will be valid IPv4 addresses in the form of strings. The last address will always be greater than the first one.
+
+Examples
+* With input "10.0.0.0", "10.0.0.50"  => return   50 
+* With input "10.0.0.0", "10.0.1.0"   => return  256 
+* With input "20.0.0.10", "20.0.1.0"  => return  246

5kyu/count-ip-addresses/solution.ts

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+/**
+ * Regards an IP address as a number with 4 digits.
+ * Each digit can be between 0 and 255.
+ * The result of this function is the total number of possible IPs 'lower' than the given IP.
+ */
+const ipToNum = (ip: string): number => {
+  const digits = ip.split('.').map(Number) as [number, number, number, number];
+  console.log(digits);
+  if(digits.length !== 4) {
+    throw new Error('Invalid IP address');
+  }
+  return digits.reduce((sum, digit) => sum * 256 + digit, 0);
+}
+
+export function ipsBetween(start: string, end: string): number {
+  return ipToNum(end) - ipToNum(start);
+}

5kyu/count-ip-addresses/tests.ts

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+// See https://www.chaijs.com for how to use Chai.
+import { assert } from "chai";
+import { ipsBetween } from "./solution";
+
+// TODO Add your tests here
+describe("example", function() {
+  it("test", function() {
+    assert.equal(ipsBetween("10.0.0.0", "10.0.0.50"), 50, 'ipsBetween("10.0.0.0", "10.0.0.50")');
+    assert.equal(ipsBetween("20.0.0.10", "20.0.1.0"), 246, 'ipsBetween("20.0.0.10", "20.0.1.0")');
+  });
+});