Add Hamming.

src/algorithms/string/hamming-distance/hammingDistance.js

@@ -0,0 +1,20 @@
+/**
+ * @param {string} a
+ * @param {string} b
+ * @return {number}
+ */
+export default function hammingDistance(a, b) {
+  if (a.length !== b.length) {
+    throw new Error('Strings must be of the same length');
+  }
+
+  let distance = 0;
+
+  for (let i = 0; i < a.length; i += 1) {
+    if (a[i] !== b[i]) {
+      distance += 1;
+    }
+  }
+
+  return distance;
+}