lintcode-binarysearch-first-bad-version

https://www.lintcode.com/problem/first-bad-version/description
【思路】ooxx找第一个符合条件的位置，二分法
/**
 * class SVNRepo {
 *     public:
 *     static bool isBadVersion(int k);
 * }
 * you can use SVNRepo::isBadVersion(k) to judge whether 
 * the kth code version is bad or not.
*/
class Solution {
public:
    /**
     * @param n: An integers.
     * @return: An integer which is the first bad version.
     */
    int findFirstBadVersion(int n) {
        int start = 1, end = n; //从第1个开始找，根据题目含义n最小为1
        while (start + 1 < end) {
            int mid = start + (end - start) / 2;
            if (SVNRepo::isBadVersion(mid)) {//查看mid处的版本
                end = mid;  //  mid已坏，左移
            } else {
                start = mid;//否则右移 //若写mid+1，在n = 2147483647 会报错，应该是int越界超过最大数
                //或当n等于INT MAX的时候会溢出超时， 把start和end改成long就可以了
            }
        }
        
        if (SVNRepo::isBadVersion(start)) {
            return start;
        }
        return end;//根据题目要求一定有坏的情况， 所以最后查找的时候不是start就是end
    }
};