278. First Bad Version

278. First Bad Version (#1 ).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 begin = 0, end = n, mid;
        
        while(begin < end) {
            mid = begin + (end - begin) / 2;
            
            if(isBadVersion(mid)) {
                end = mid;  //Ensure there is at least one bad version in the range. Also end will move at least one step.
            } else {
                begin = mid + 1;  //begin will move at least one step.
            }
        }
        //start == end == mid
        return start;
    }
}