278. First Bad Version

题目：https://leetcode.com/problems/first-bad-version/

代码：

/* 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 pre = 0;        int last = n;        while(pre<last)        {            int cur = pre + (last-pre)/2; // not same as (pre+last)/2,  this is where i am wrong;            if(isBadVersion(cur))            {                last = cur;            }            else            {                pre = cur+1;            }        }        return pre;    }}18ms