leetcode278

/* The isBadVersion API is defined in the parent class VersionControl.
      bool IsBadVersion(int version); */

public class Solution : VersionControl {
    public int FirstBadVersion(int n) {
        var start = 1;
            var end = n;
            while (start < end)
            {
                var mid = start + (end - start) / 2;
                if (!IsBadVersion(mid))
                {
                    start = mid + 1;
                }
                else
                {
                    end = mid;
                }                
            }
            return start;
    }
}