Add solution #420

Author: JoshCrozier

README.md

@@ -335,6 +335,7 @@
 416|[Partition Equal Subset Sum](./0416-partition-equal-subset-sum.js)|Medium|
 417|[Pacific Atlantic Water Flow](./0417-pacific-atlantic-water-flow.js)|Medium|
 419|[Battleships in a Board](./0419-battleships-in-a-board.js)|Medium|
+420|[Strong Password Checker](./0420-strong-password-checker.js)|Hard|
 434|[Number of Segments in a String](./0434-number-of-segments-in-a-string.js)|Easy|
 435|[Non-overlapping Intervals](./0435-non-overlapping-intervals.js)|Medium|
 437|[Path Sum III](./0437-path-sum-iii.js)|Medium|

solutions/0420-strong-password-checker.js

@@ -0,0 +1,60 @@
+/**
+ * 420. Strong Password Checker
+ * https://leetcode.com/problems/strong-password-checker/
+ * Difficulty: Hard
+ *
+ * A password is considered strong if the below conditions are all met:
+ * - It has at least 6 characters and at most 20 characters.
+ * - It contains at least one lowercase letter, at least one uppercase letter, and at
+ *   least one digit.
+ * - It does not contain three repeating characters in a row (i.e., "Baaabb0" is weak,
+ *   but "Baaba0" is strong).
+ *
+ * Given a string password, return the minimum number of steps required to make password
+ * strong. if password is already strong, return 0.
+ *
+ * In one step, you can:
+ * - Insert one character to password,
+ * - Delete one character from password, or
+ * - Replace one character of password with another character.
+ */
+
+/**
+ * @param {string} password
+ * @return {number}
+ */
+var strongPasswordChecker = function(password) {
+  const types = 3 - (/[a-z]/.test(password) + /[A-Z]/.test(password) + /[0-9]/.test(password));
+  let replacements = 0;
+  let modOneCount = 0;
+  let modTwoCount = 0;
+
+  if (password.length < 6) {
+    return Math.max(6 - password.length, types);
+  }
+
+  for (let i = 0; i < password.length;) {
+    let j = i;
+    while (j < password.length && password[j] === password[i]) {
+      j++;
+    }
+    const repeatLength = j - i;
+    if (repeatLength >= 3) {
+      replacements += Math.floor(repeatLength / 3);
+      if (repeatLength % 3 === 0) modOneCount++;
+      if (repeatLength % 3 === 1) modTwoCount++;
+    }
+    i = j;
+  }
+
+  if (password.length <= 20) {
+    return Math.max(types, replacements);
+  }
+
+  const deletions = password.length - 20;
+  replacements -= Math.min(deletions, modOneCount);
+  replacements -= Math.min(Math.max(deletions - modOneCount, 0), modTwoCount * 2) / 2;
+  replacements -= Math.max(deletions - modOneCount - modTwoCount * 2, 0) / 3;
+
+  return deletions + Math.max(types, Math.max(0, Math.ceil(replacements)));
+};