Add string check anagram (TheAlgorithms#254)

* Add CheckAnagram.js to String Algorithms that checks if Strings are anagrams

* Add CheckAnagram.js to String Algorithms that checks if Strings are anagrams

* Add CheckAnagram.js to String Algorithms that checks if Strings are anagrams

Author: techieParth

String/CheckAnagram.js

@@ -0,0 +1,50 @@
+// Anagram check is case sensitive; i.e. Aba and aba is not a anagram.
+// inputs are strings i.e. str1 and str2
+const checkAnagram = (str1, str2) => {
+  // check that inputs are strings.
+  if (typeof str1 !== 'string' || typeof str2 !== 'string') {
+    return 'Not string(s)'
+  }
+
+  // If both strings have not same lengths then they can not be anagram.
+  if (str1.length !== str2.length) {
+    return 'Not Anagram'
+  }
+
+  // Use hashmap to keep count of characters in str1
+
+  const str1CharCount = new Map()
+
+  for (let i = 0; i < str1.length; i++) {
+    let previousCount = 0
+    if (str1CharCount.has(str1[i])) {
+      previousCount = str1CharCount.get(str1[i])
+    }
+    str1CharCount.set(str1[i], previousCount + 1)
+  }
+
+  // Now check if second string has same characters?
+
+  for (let i = 0; i < str2.length; i++) {
+    let previousCount = 0
+    // if str1CharCount has no key for str2[i] then not anagram.
+    if (!str1CharCount.has(str2[i])) {
+      return 'Not anagrams'
+    }
+    previousCount = str1CharCount.get(str2[i])
+    str1CharCount.set(str2[i], previousCount - 1)
+  }
+
+  // Now check if all entries in hashmap has zeros.
+
+  for (const key in str1CharCount) {
+    if (str1CharCount[key] !== 0) { return 'Not anagrams' }
+  }
+
+  return 'Anagrams'
+}
+
+console.log(checkAnagram('abcd', 'bcad')) // should print anagram
+console.log(checkAnagram('abcd', 'abef')) // should print not anagram
+console.log(checkAnagram(10, 'abcd'))// should print Not String(s).
+console.log(checkAnagram('abs', 'abds'))// should print not anagram