今日簡單題：https://leetcode-cn.com/problems/first-bad-version/

比較清晰的二分法，關(guān)注下while不要死循環(huán)即可。
另外吐槽一下題解，mid=head+(tail-head)/2; 那不就是mid=(head+tail)/2嗎？這個(gè)還更直觀，就是中位數(shù)。

貼下代碼：

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

public class Solution extends VersionControl {
    public int firstBadVersion(int n) {
        int head = 1;
        int tail = n;
        int tmp = (head+tail)/2;
        while(head < tail) {  
            // 如果tmp是壞版本，那第一個(gè)壞版本一定在它左邊
            if (isBadVersion(tmp)) {
                tail = tmp;
            }
            else {
                head = tmp + 1;
            }
            tmp = (head+tail)/2;
        }
        return head;
    }
}