Add solution #301

Author: JoshCrozier

README.md

@@ -246,6 +246,7 @@
 297|[Serialize and Deserialize Binary Tree](./0297-serialize-and-deserialize-binary-tree.js)|Hard|
 299|[Bulls and Cows](./0299-bulls-and-cows.js)|Medium|
 300|[Longest Increasing Subsequence](./0300-longest-increasing-subsequence.js)|Medium|
+301|[Remove Invalid Parentheses](./0301-remove-invalid-parentheses.js)|Hard|
 303|[Range Sum Query - Immutable](./0303-range-sum-query-immutable.js)|Easy|
 306|[Additive Number](./0306-additive-number.js)|Medium|
 309|[Best Time to Buy and Sell Stock with Cooldown](./0309-best-time-to-buy-and-sell-stock-with-cooldown.js)|Medium|

solutions/0301-remove-invalid-parentheses.js

@@ -0,0 +1,48 @@
+/**
+ * 301. Remove Invalid Parentheses
+ * https://leetcode.com/problems/remove-invalid-parentheses/
+ * Difficulty: Hard
+ *
+ * Given a string s that contains parentheses and letters, remove the minimum number of
+ * invalid parentheses to make the input string valid.
+ *
+ * Return a list of unique strings that are valid with the minimum number of removals.
+ * You may return the answer in any order.
+ */
+
+/**
+ * @param {string} s
+ * @return {string[]}
+ */
+var removeInvalidParentheses = function(s) {
+  const result = new Set();
+  let minRemoved = Infinity;
+
+  backtrack(s, 0, 0, 0, 0, '');
+
+  return Array.from(result);
+
+  function backtrack(str, index, open, close, removed, curr) {
+    if (index === s.length) {
+      if (open === close && removed <= minRemoved) {
+        if (removed < minRemoved) {
+          result.clear();
+          minRemoved = removed;
+        }
+        result.add(curr);
+      }
+      return;
+    }
+
+    if (s[index] !== '(' && s[index] !== ')') {
+      backtrack(str, index + 1, open, close, removed, curr + s[index]);
+    } else {
+      backtrack(str, index + 1, open, close, removed + 1, curr);
+      if (s[index] === '(') {
+        backtrack(str, index + 1, open + 1, close, removed, curr + '(');
+      } else if (close < open) {
+        backtrack(str, index + 1, open, close + 1, removed, curr + ')');
+      }
+    }
+  }
+};