Add solution #278

Author: JoshCrozier

Diff for: README.md

@@ -96,6 +96,7 @@
 264|[Ugly Number II](./0264-ugly-number-ii.js)|Medium|
 268|[Missing Number](./0268-missing-number.js)|Easy|
 273|[Integer to English Words](./0273-integer-to-english-words.js)|Hard|
+278|[First Bad Version](./0278-first-bad-version.js)|Medium|
 283|[Move Zeroes](./0283-move-zeroes.js)|Easy|
 326|[Power of Three](./0326-power-of-three.js)|Easy|
 342|[Power of Four](./0342-power-of-four.js)|Easy|

Diff for: solutions/0278-first-bad-version.js

@@ -0,0 +1,43 @@
+/**
+ * 278. First Bad Version
+ * https://leetcode.com/problems/first-bad-version/
+ * Difficulty: Medium
+ *
+ * You are a product manager and currently leading a team to develop a new product.
+ * Unfortunately, the latest version of your product fails the quality check. Since
+ * each version is developed based on the previous version, all the versions after
+ * a bad version are also bad.
+ *
+ * Suppose you have n versions [1, 2, ..., n] and you want to find out the first bad
+ * one, which causes all the following ones to be bad.
+ *
+ * You are given an API bool isBadVersion(version) which returns whether version is
+ * bad. Implement a function to find the first bad version. You should minimize the
+ * number of calls to the API.
+ */
+
+/**
+ * @param {function} isBadVersion()
+ * @return {function}
+ */
+var solution = function(isBadVersion) {
+  /**
+   * @param {integer} n Total versions
+   * @return {integer} The first bad version
+   */
+  return n => {
+    let left = 1;
+    let right = n;
+
+    while (left <= right) {
+      const pivot = Math.floor((right + left) / 2);
+      if (isBadVersion(pivot)) {
+        right = pivot - 1;
+      } else {
+        left = pivot + 1;
+      }
+    }
+
+    return left;
+  };
+};