278. First Bad Version.cs

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

public class Solution : VersionControl {
    public int FirstBadVersion(int n) {
        if (n == 0) return 0;
        int start = 1;
        int end = n;
        while (start + 1 < end) {
            int mid = start + (end - start) / 2;
            if (IsBadVersion(mid)) {
                end = mid;
            } else {
                start = mid;
            }
        }
        if (IsBadVersion(start)) return start;
        return end;
    }
}