algorithm: first unique char in a string (#1103)

* feat: Added Algo first unique char in a string.

* Optimised algo to linear time complexity

* removed double quotes

* Review changes: if-else logic

Author: 10kartik

DIRECTORY.md

@@ -299,6 +299,7 @@
   * [CountVowels](String/CountVowels.js)
   * [CreatePermutations](String/CreatePermutations.js)
   * [DiceCoefficient](String/DiceCoefficient.js)
+  * [FirstUniqueCharacter](String/FirstUniqueCharacter.js)
   * [FormatPhoneNumber](String/FormatPhoneNumber.js)
   * [GenerateGUID](String/GenerateGUID.js)
   * [HammingDistance](String/HammingDistance.js)

String/FirstUniqueCharacter.js

@@ -0,0 +1,30 @@
+/**
+ * @function firstUniqChar
+ * @description Given a string str, find the first non-repeating character in it and return its index. If it does not exist, return -1.
+ * @param {String} str - The input string
+ * @return {Number} - The index of first unique character.
+ * @example firstUniqChar("javascript") => 0
+ * @example firstUniqChar("sesquipedalian") => 3
+ * @example firstUniqChar("aabb") => -1
+ */
+
+const firstUniqChar = (str) => {
+  if (typeof str !== 'string') {
+    throw new TypeError('Argument should be string')
+  }
+  const count = new Map()
+
+  for (const char of str) {
+    if (!count[char]) {
+      count[char] = 1
+    } else {
+      count[char]++
+    }
+  }
+  for (let i = 0; i < str.length; i++) {
+    if (count[str[i]] === 1) return i
+  }
+  return -1
+}
+
+export { firstUniqChar }

String/test/FirstUniqueCharacter.test.js

@@ -0,0 +1,9 @@
+import { firstUniqChar } from '../FirstUniqueCharacter'
+
+describe('firstUniqChar', () => {
+  it('locates the index of first unique character in the string', () => {
+    expect(firstUniqChar('javascript')).toEqual(0)
+    expect(firstUniqChar('sesquipedalian')).toEqual(3)
+    expect(firstUniqChar('aabb')).toEqual(-1)
+  })
+})