add solution of problem 278: first bad version

Author: ppulse

FirstBadVersion278/README.md

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+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 will return whether `version` is bad. Implement a function to find the first bad version. You should minimize the number of calls to the API.

FirstBadVersion278/Solution.java

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+/* The isBadVersion API is defined in the parent class VersionControl.
+      boolean isBadVersion(int version); */
+
+public class Solution extends VersionControl {
+    public int firstBadVersion(int n) {
+        int left = 1;
+        long right = n;
+        
+        while (left <= right) {
+            int mid = (int)((left + right) >> 1);
+            if (isBadVersion(mid)) {
+                right = mid - 1;
+            } else {
+                left = mid + 1;
+            }
+        }
+        
+        return left;
+    }
+}