solve 278.first-bad-version

Author: andavid

vscode/278.first-bad-version.java

@@ -0,0 +1,58 @@
+/*
+ * @lc app=leetcode id=278 lang=java
+ *
+ * [278] First Bad Version
+ *
+ * https://leetcode.com/problems/first-bad-version/description/
+ *
+ * algorithms
+ * Easy (28.99%)
+ * Total Accepted:    215.1K
+ * Total Submissions: 727.9K
+ * Testcase Example:  '5\n4'
+ *
+ * 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.
+ *
+ * Example:
+ *
+ *
+ * Given n = 5, and version = 4 is the first bad version.
+ *
+ * call isBadVersion(3) -> false
+ * call isBadVersion(5) -> true
+ * call isBadVersion(4) -> true
+ *
+ * Then 4 is the first bad version. 
+ *
+ */
+/* 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;
+    int right = n;
+
+    while (left < right) {
+      int mid = left + (right - left) / 2;
+      if (isBadVersion(mid)) {
+        right = mid;
+      } else {
+        left = mid + 1;
+      }
+    }
+
+    return left;
+  }
+}
+