Add solution #316

Author: JoshCrozier

README.md

@@ -114,6 +114,7 @@
 278|[First Bad Version](./0278-first-bad-version.js)|Medium|
 283|[Move Zeroes](./0283-move-zeroes.js)|Easy|
 290|[Word Pattern](./0290-word-pattern.js)|Easy|
+316|[Remove Duplicate Letters](./0316-remove-duplicate-letters.js)|Medium|
 326|[Power of Three](./0326-power-of-three.js)|Easy|
 342|[Power of Four](./0342-power-of-four.js)|Easy|
 344|[Reverse String](./0344-reverse-string.js)|Easy|

solutions/0316-remove-duplicate-letters.js

@@ -0,0 +1,29 @@
+/**
+ * 316. Remove Duplicate Letters
+ * https://leetcode.com/problems/remove-duplicate-letters/
+ * Difficulty: Medium
+ *
+ * Given a string s, remove duplicate letters so that every letter appears once and only once. You must make sure your result is
+ * the smallest in lexicographical order among all possible results.
+ */
+
+/**
+ * @param {string} s
+ * @return {string}
+ */
+var removeDuplicateLetters = function(s) {
+  const stack = [];
+
+  for (let i = 0; i < s.length; i++) {
+    const letter = s[i];
+    if (stack.indexOf(letter) > -1) {
+      continue;
+    }
+    while (stack.length > 0 && stack[stack.length - 1] > letter && s.indexOf(stack[stack.length - 1], i) > i) {
+      stack.pop();
+    }
+    stack.push(letter);
+  }
+
+  return stack.join('');
+};