Add exercise 1.1 book solution.

Author: Isaac Ramirez

src/chapters/01/exercises/is-unique/book-solution/is-unique.solution.js

@@ -0,0 +1,21 @@
+/**
+ * Using a hash-table.
+ * Running time: O(N)
+ * @param {string} str
+ * @returns {boolean}
+ */
+function isUniqueChars(str) {
+  const charSet = {};
+
+  for (let i = 0; i < str.length; i++) {
+    const code = str.charCodeAt(i);
+
+    if (charSet[code]) return false;
+
+    charSet[code] = true;
+  }
+
+  return true;
+}
+
+module.exports = isUniqueChars;

src/chapters/01/exercises/is-unique/index.js

@@ -1,3 +1,6 @@
+/*  Book solutions */
+const isUniqueSolution = require("./book-solution/is-unique.solution");
+/* My solutions */
 const isUniqueV1 = require("./my-solution/is-unique.v1");
 
 /* Export the solution to be tested */