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278-first-bad-version/278-first-bad-version.go

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+/** 
+ * Forward declaration of isBadVersion API.
+ * @param   version   your guess about first bad version
+ * @return 	 	      true if current version is bad 
+ *			          false if current version is good
+ * func isBadVersion(version int) bool;
+ */
+
+func firstBadVersion(n int) int {
+    // binary search iterative
+
+    left, right := 1, n
+
+    for left <= right {
+        pivot := left + (right - left)/2
+
+        if isBadVersion(pivot) == true && pivot == 1 {
+            return 1
+        } else if isBadVersion(pivot) == true && isBadVersion(pivot - 1) == false {
+            return pivot
+        }
+
+        if isBadVersion(pivot) == false {
+            left = pivot + 1    
+        } else {
+            right = pivot - 1
+        }
+    }
+
+    return 1
+}