FirstBadVersion.java

package easy;
/**
 * ClassName: FirstBadVersion.java
 * Author: chenyiAlone
 * Create Time: 2019/5/16 11:03
 * Description: No.278
 * 思路:
 *      Binary Search 相同的最左边元素
 *
 *
 *
 * 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.
 */
public class FirstBadVersion {
    public int firstBadVersion(int n) {
        int l = 1, r = n;
        while (l <= r) {
            int mid = l + (r - l) >> 1;
            if (!isBadVersion(mid))
                l = mid + 1;
            else
                r = mid - 1;
        }
        return l;
    }
    private boolean isBadVersion(int i) {
        return true;
    }
}