Implement first non-repeating character problem

Author: sudheerj

src/javascript/algorithms/hashtable/firstNonRepeatingCharacter.js

@@ -0,0 +1,59 @@
+function firstNonRepeatingCharWithMap(inputStr) {
+    if(inputStr.length === 0) return null;
+    let charCountsMap = new Map();
+    for(let ch of inputStr) {
+        charCountsMap.set(ch, (charCountsMap.get(ch) || 0) + 1);
+    }
+    
+    for(let [key, value] of charCountsMap.entries()) {
+        if(value === 1) {
+            return key;
+        }
+    }
+    return null;
+}
+
+function firstNonRepeatingCharWithObj(inputStr) {
+    if(inputStr.length === 0) return null;
+    let charCountsObj = {};
+    for(let ch of inputStr) {
+        charCountsObj[ch] = (charCountsObj[ch] || 0) + 1;
+    }
+    
+    for(let [key, value] of Object.entries(charCountsObj)) {
+        if(value === 1) {
+            return key;
+        }
+    }
+    return null;
+}
+
+
+
+/**---------------
+   All Unique
+   --------------- */
+console.log("Input: 'abcdefgh'");
+console.log("Output: ", firstNonRepeatingCharWithObj('abcdefgh'));
+console.log("---------------");
+
+/**---------------
+   Some Duplicates
+   --------------- */
+console.log("Input: 'abccddefgggh'");
+console.log("Output: ", firstNonRepeatingCharWithObj('abccddefgggh'));
+console.log("---------------");
+
+/** ---------------
+    All Duplicates
+    --------------- */
+console.log("Input: 'aabbccdddeeeff'");
+console.log("Output: ", firstNonRepeatingCharWithMap('aabbccdddeeeff'));
+console.log("---------------");
+
+/** ---------------
+    Empty String
+    --------------- */
+console.log("Input: ''");
+console.log("Output: ", firstNonRepeatingMap(''));
+console.log("---------------");