init(Easy/Hash Table): add solution for 387.first-unique-character-in-a-string.js

Easy/Hash Table/387.first-unique-character-in-a-string.js

@@ -0,0 +1,59 @@
+/*
+ * 387. First Unique Character in a String
+ * Difficulty: Easy
+ * https://leetcode.com/problems/first-unique-character-in-a-string/
+ *
+ * ──────────────────────────────────────────────────
+ *
+ * Given a string s, find the first non-repeating character in it and
+ * return its index. If it does not exist, return -1.
+ *
+ *
+ *
+ * Example 1:
+ *
+ * Input: s = "leetcode"
+ *
+ * Output: 0
+ *
+ * Explanation:
+ *
+ * The character 'l' at index 0 is the first character that does not
+ * occur at any other index.
+ *
+ * Example 2:
+ *
+ * Input: s = "loveleetcode"
+ *
+ * Output: 2
+ *
+ * Example 3:
+ *
+ * Input: s = "aabb"
+ *
+ * Output: -1
+ *
+ *
+ *
+ * Constraints:
+ *
+ * 	• 1 <= s.length <= 10^5
+ *
+ * 	• s consists of only lowercase English letters.
+ */
+
+/**
+ * @param {string} s
+ * @return {number}
+ */
+var firstUniqChar = function (s) {
+  const freq = {};
+  for (let c of s) freq[c] = (freq[c] || 0) + 1;
+
+  for (let i = 0; i < s.length; i++) {
+    if (freq[s[i]] === 1) {
+      return i;
+    }
+  }
+  return -1;
+};