add sol

leetcode/BinarySearch/278.FirstBadVersion/sol.go

@@ -0,0 +1,34 @@
+// https://leetcode.com/problems/first-bad-version
+
+package main
+
+import (
+	"fmt"
+)
+
+// Assume this is a pre-defined API that checks if a version is bad
+var firstBad int
+
+func isBadVersion(version int) bool {
+	return version >= firstBad
+}
+
+// FirstBadVersion finds the first bad version among n versions
+func firstBadVersion(n int) int {
+	left, right := 1, n
+	for left < right {
+		mid := left + (right-left)>>1
+		if isBadVersion(mid) {
+			right = mid
+		} else {
+			left = mid + 1
+		}
+	}
+	return left
+}
+
+func main() {
+	n := 5
+	firstBad = 4
+	fmt.Println(firstBadVersion(n))
+}