Remove Invalid Parentheses

Author: charlesbuczel

0301_removeInvalidParentheses.js

@@ -0,0 +1,67 @@
+let validExpressions, minimumRemoved, expression, input, length;
+
+/**
+ * @param {string} s String containing parentheses ().
+ * @return {string[]} List of all possible results.
+ * @summary Remove Invalid Parentheses {@link https://leetcode.com/problems/remove-invalid-parentheses/}
+ * @description Remove the minimum number of invalid parentheses in order to make the input string valid.
+ * Space O(n) - on recurrsion maximum call stack depth will be n.
+ * Time O(2^n) - each step can generate up to two more paths (remoeve or keep parentheses).
+ */
+const removeInvalidParentheses = s => {
+  validExpressions = {};
+  minimumRemoved = Number.MAX_SAFE_INTEGER;
+  expression = [];
+  input = s;
+  length = input.length;
+
+  let openRemoveCount = 0;
+  let closeRemoveCount = 0;
+  for (let index = 0; index < length; index++) {
+    if (s[index] === '(') openRemoveCount++;
+    else if (s[index] === ')') {
+      if (openRemoveCount === 0) closeRemoveCount++;
+      if (openRemoveCount > 0) openRemoveCount--;
+    }
+  }
+
+  removeMinimumParentheses(0, 0, 0, openRemoveCount, closeRemoveCount);
+
+  return Object.keys(validExpressions);
+};
+
+/**
+ * @param {number} i Current index.
+ * @param {number} openCount Number of open parentheses '(' for currently tested solution.
+ * @param {number} closeCount Number of close parentheses ')' for currently tested solution.
+ * @param {number} minOpen Remaining count of open parentheses to be removed for optimal solution.
+ * @param {number} minClose Remaining count of close parentheses to be removed for optimal solution.
+ * @return {undefined} Actual solution is written to validExpressions.
+ */
+const removeMinimumParentheses = (i, openCount, closeCount, minOpen, minClose) => {
+  if (i === length && !minOpen && !minClose) {
+    const solution = expression.join('');
+    validExpressions[solution] = true;
+  } else if (i < length) {
+    const char = input[i];
+
+    if (char === '(' && minOpen > 0) {
+      removeMinimumParentheses(i + 1, openCount, closeCount, minOpen - 1, minClose);
+    }
+    if (char === ')' && minClose > 0) {
+      removeMinimumParentheses(i + 1, openCount, closeCount, minOpen, minClose - 1);
+    }
+
+    expression.push(char);
+
+    if (char !== '(' && char !== ')') {
+      removeMinimumParentheses(i + 1, openCount, closeCount, minOpen, minClose);
+    } else if (char === '(') {
+      removeMinimumParentheses(i + 1, openCount + 1, closeCount, minOpen, minClose);
+    } else if (closeCount < openCount) {
+      removeMinimumParentheses(i + 1, openCount, closeCount + 1, minOpen, minClose);
+    }
+
+    expression.pop();
+  }
+};