LeetCode First Bad Version

原题链接在这里：https://leetcode.com/problems/first-bad-version/

尽可能少的使用API, 就想到Binary Search. 查中点是不是，若是bad version, 就在左边继续查，若不是bad version, 就在右边继续查找。

Note:　　求中点mid时，要用 mid = left +(right - left)/2, 不能使用 mid = (left + right)/2 因为loop 过程中(left + right)可能超过 Integer.MAX_VALUE, overflow了。

AC Java:

/* 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 left = 1;
int right = n;
int res = 0;
while(left<=right){
int mid = left + (right - left)/2;
if(isBadVersion(mid)){
right = mid-1;
}else{
left = mid+1;
}
}
return left;
}
}