Add solution #400

Author: JoshCrozier

README.md

@@ -318,6 +318,7 @@
 397|[Integer Replacement](./0397-integer-replacement.js)|Medium|
 398|[Random Pick Index](./0398-random-pick-index.js)|Medium|
 399|[Evaluate Division](./0399-evaluate-division.js)|Medium|
+400|[Nth Digit](./0400-nth-digit.js)|Medium|
 404|[Sum of Left Leaves](./0404-sum-of-left-leaves.js)|Easy|
 405|[Convert a Number to Hexadecimal](./0405-convert-a-number-to-hexadecimal.js)|Easy|
 407|[Trapping Rain Water II](./0407-trapping-rain-water-ii.js)|Hard|

solutions/0400-nth-digit.js

@@ -0,0 +1,24 @@
+/**
+ * 400. Nth Digit
+ * https://leetcode.com/problems/nth-digit/
+ * Difficulty: Medium
+ *
+ * Given an integer n, return the nth digit of the infinite integer sequence
+ * [1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, ...].
+ */
+
+/**
+ * @param {number} n
+ * @return {number}
+ */
+var findNthDigit = function(n) {
+  let total = 1;
+  let start = 1;
+
+  for (let count = 9; n > total * count; total++, count *= 10, start *= 10) {
+    n -= total * count;
+  }
+
+  start += Math.floor((n - 1) / total);
+  return +(start.toString()[(n - 1) % total]);
+};