May_01_First_Bad_Versioncpp

class Solution {
public:
    int firstBadVersion(int n) {
        int index;
        int low=0;
        int high=n;
        int mid;
        while(low<=high)
        {
            mid=low+(high-low)/2;
            if(isBadVersion(mid))
            {
                index=mid;
                high=mid-1;
            }
            else
            {
                low=mid+1;
            }
        }
        return index;
    }
};