bad version

Author: volodimyr

278.first_bad_version/bad.go

@@ -0,0 +1,52 @@
+// 278. First bad version
+// Topics: 'Binary Search', 'Interactive'
+
+// 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.
+
+// Example 1:
+
+// Input: n = 5, bad = 4
+// Output: 4
+// Explanation:
+// call isBadVersion(3) -> false
+// call isBadVersion(5) -> true
+// call isBadVersion(4) -> true
+// Then 4 is the first bad version.
+
+// Example 2:
+
+// Input: n = 1, bad = 1
+// Output: 1
+
+// Constraints:
+
+//     1 <= bad <= n <= 231 - 1
+
+package firstbadversion
+
+func firstBadVersion(n int) int {
+	L, R := 0, n
+
+	var bad int
+	for L <= R {
+		mid := L + (R-L)/2
+		isBad := isBadVersion(mid)
+
+		if isBad {
+			bad = mid
+			R = mid - 1
+		} else {
+			L = mid + 1
+		}
+	}
+	return bad
+}
+
+func isBadVersion(v int) bool {
+	// dummy
+	return false
+}