Added algorithm CheckHeterogram

String/CheckHeterogram.js

@@ -0,0 +1,40 @@
+// A [Heterogram](https://en.wikipedia.org/wiki/Heterogram_(literature)) is a word, phrase or sentence in which no letter of the alphabet occurs more than once.
+
+/**
+ * @function checkHeterogram
+ * @param {string} str
+ * @returns {boolean}
+ * @description - check if a string is a heterogram
+ * @example - checkHeterogram('hero') => true
+ * @example - checkHeterogram('CoMpUtEr') => true
+ * @example - checkHeterogram('Great work!!') => true
+ * @example - checkHeterogram('Aba') => false
+ */
+
+const checkHeterogram = (str) => {
+  // Check that input is a string
+  if (typeof str !== 'string') {
+    throw new TypeError('Argument not a string.')
+  }
+
+  // initialize a hashmap where the letters of the string will be checked for duplicates
+  const letters = new Map()
+
+  // Check all the characters in the string by looping through it
+  for (let i = 0; i < str.length; i++) {
+    // If the character is a letter check whether it is a duplicate
+    if (str.charAt(i).match(/[a-z]/gi)) {
+      // If the letter exists in the hashmap already return false else store it in the hashmap
+      if (letters.has(str.charAt(i).toLowerCase())) {
+        return false
+      } else {
+        letters.set(str.charAt(i).toLowerCase())
+      }
+    }
+  }
+
+  // Once all characters of the string have been checked return true
+  return true
+}
+
+export { checkHeterogram }

String/test/CheckHeterogram.test.js

@@ -0,0 +1,31 @@
+import { checkHeterogram } from '../CheckHeterogram'
+
+describe('Testing checkHeterogram', () => {
+  it('expects to throw type error if given a non string argument', () => {
+    expect(() => checkHeterogram(0)).toThrow()
+  })
+  it('expects to throw type error if given a non string argument', () => {
+    expect(() => checkHeterogram(true)).toThrow()
+  })
+  it('expects to return true if the argument is a heterogram', () => {
+    expect(checkHeterogram('hero')).toBe(true)
+  })
+  it('expects to return true if the given argument only contains non-alphabetic characters', () => {
+    expect(checkHeterogram('!!..&&  ??22')).toBe(true)
+  })
+  it('expects to return true if the given string is a heterogram which contains duplicate non-alphabetic characters', () => {
+    expect(checkHeterogram('C, o, m, p, u, t, e, r!!')).toBe(true)
+  })
+  it('expects to return true if the given string is empty', () => {
+    expect(checkHeterogram('')).toBe(true)
+  })
+  it('expects to return true if the given string contains multiple spaces and is a heterogram', () => {
+    expect(checkHeterogram('Cwm fjord bank glyphs vext quiz')).toBe(true)
+  })
+  it('expects to return false if the given string contains duplicate letters with differing case (case insensitive)', () => {
+    expect(checkHeterogram('Ada')).toBe(false)
+  })
+  it('expects to return false if the given string contains duplicate letters in different words', () => {
+    expect(checkHeterogram('List duplicates')).toBe(false)
+  })
+})