Add solution #233

Author: JoshCrozier

README.md

@@ -204,6 +204,7 @@
 229|[Majority Element II](./0229-majority-element-ii.js)|Medium|
 231|[Power of Two](./0231-power-of-two.js)|Easy|
 232|[Implement Queue using Stacks](./0232-implement-queue-using-stacks.js)|Easy|
+233|[Number of Digit One](./0233-number-of-digit-one.js)|Hard|
 234|[Palindrome Linked List](./0234-palindrome-linked-list.js)|Easy|
 235|[Lowest Common Ancestor of a Binary Search Tree](./0235-lowest-common-ancestor-of-a-binary-search-tree.js)|Easy|
 236|[Lowest Common Ancestor of a Binary Tree](./0236-lowest-common-ancestor-of-a-binary-tree.js)|Medium|

solutions/0233-number-of-digit-one.js

@@ -0,0 +1,26 @@
+/**
+ * 233. Number of Digit One
+ * https://leetcode.com/problems/number-of-digit-one/
+ * Difficulty: Hard
+ *
+ * Given an integer n, count the total number of digit 1 appearing in all non-negative
+ * integers less than or equal to n.
+ */
+
+/**
+ * @param {number} n
+ * @return {number}
+ */
+var countDigitOne = function(n) {
+  if (n <= 0) {
+    return 0;
+  } else if (n < 10) {
+    return 1;
+  }
+
+  const base = 10 ** (n.toString().length - 1);
+  const answer = parseInt(n / base);
+
+  return countDigitOne(base - 1) * answer
+    + (answer === 1 ? (n - base + 1) : base) + countDigitOne(n % base);
+};