278.first-bad-version.cs

/*
 * @lc app=leetcode id=278 lang=csharp
 *
 * [278] First Bad Version
 *
 * https://leetcode.com/problems/first-bad-version/description/
 *
 * algorithms
 * Easy (34.86%)
 * Likes:    1321
 * Dislikes: 643
 * Total Accepted:    404K
 * Total Submissions: 1.2M
 * Testcase Example:  '5\n4'
 *
 * 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 will return whether
 * version is bad. Implement a function to find the first bad version. You
 * should minimize the number of calls to the API.
 *
 * Example:
 *
 *
 * Given n = 5, and version = 4 is the first bad version.
 *
 * call isBadVersion(3) -> false
 * call isBadVersion(5) -> true
 * call isBadVersion(4) -> true
 *
 * Then 4 is the first bad version. 
 *
 *
 */
namespace _278
{
    // @lc code=start
    /* The isBadVersion API is defined in the parent class VersionControl.
          bool IsBadVersion(int version); */

    // public class Solution : VersionControl {
    public class Solution : VersionControl
    {
        public int FirstBadVersion(int n)
        {
            var left = 0;
            var right = n;
            while (left < right)
            {
                var mid = left + (right - left) / 2; // this avoids overflow
                if (IsBadVersion(mid))
                {
                    right = mid;
                }
                else
                {
                    left = mid + 1;
                }
            }
            return left;
        }
    }
    // @lc code=end

    public class VersionControl
    {
        public bool IsBadVersion(int i) => false;
    }
}